diff --git a/blockchain/reactor.go b/blockchain/reactor.go
index 90258825e..f88bccc3d 100644
--- a/blockchain/reactor.go
+++ b/blockchain/reactor.go
@@ -251,7 +251,6 @@ FOR_LOOP:
 						// TODO This is bad, are we zombie?
 						cmn.PanicQ(cmn.Fmt("Failed to process committed block (%d:%X): %v", first.Height, first.Hash(), err))
 					}
-					bcR.state.Save()
 				}
 			}
 			continue FOR_LOOP
diff --git a/consensus/replay.go b/consensus/replay.go
index 731e7d216..bd0975f4d 100644
--- a/consensus/replay.go
+++ b/consensus/replay.go
@@ -100,27 +100,51 @@ func (cs *ConsensusState) catchupReplay(csHeight int) error {
 	cs.replayMode = true
 	defer func() { cs.replayMode = false }()
 
-	// Ensure that height+1 doesn't exist
-	gr, found, err := cs.wal.group.Search("#HEIGHT: ", makeHeightSearchFunc(csHeight+1))
-	if found {
-		return errors.New(Fmt("WAL should not contain height %d.", csHeight+1))
-	}
+	// Ensure that ENDHEIGHT for this height doesn't exist
+	// NOTE: This is just a sanity check. As far as we know things work fine without it,
+	// and Handshake could reuse ConsensusState if it weren't for this check (since we can crash after writing ENDHEIGHT).
+	gr, found, err := cs.wal.group.Search("#ENDHEIGHT: ", makeHeightSearchFunc(csHeight))
 	if gr != nil {
 		gr.Close()
 	}
+	if found {
+		return errors.New(Fmt("WAL should not contain #ENDHEIGHT %d.", csHeight))
+	}
 
-	// Search for height marker
-	gr, found, err = cs.wal.group.Search("#HEIGHT: ", makeHeightSearchFunc(csHeight))
+	// Search for last height marker
+	gr, found, err = cs.wal.group.Search("#ENDHEIGHT: ", makeHeightSearchFunc(csHeight-1))
 	if err == io.EOF {
-		log.Warn("Replay: wal.group.Search returned EOF", "height", csHeight)
-		return nil
+		log.Warn("Replay: wal.group.Search returned EOF", "#ENDHEIGHT", csHeight-1)
+		// if we upgraded from 0.9 to 0.9.1, we may have #HEIGHT instead
+		// TODO (0.10.0): remove this
+		gr, found, err = cs.wal.group.Search("#HEIGHT: ", makeHeightSearchFunc(csHeight))
+		if err == io.EOF {
+			log.Warn("Replay: wal.group.Search returned EOF", "#HEIGHT", csHeight)
+			return nil
+		} else if err != nil {
+			return err
+		}
 	} else if err != nil {
 		return err
+	} else {
+		defer gr.Close()
 	}
 	if !found {
-		return errors.New(Fmt("WAL does not contain height %d.", csHeight))
+		// if we upgraded from 0.9 to 0.9.1, we may have #HEIGHT instead
+		// TODO (0.10.0): remove this
+		gr, found, err = cs.wal.group.Search("#HEIGHT: ", makeHeightSearchFunc(csHeight))
+		if err == io.EOF {
+			log.Warn("Replay: wal.group.Search returned EOF", "#HEIGHT", csHeight)
+			return nil
+		} else if err != nil {
+			return err
+		} else {
+			defer gr.Close()
+		}
+
+		// TODO (0.10.0): uncomment
+		// return errors.New(Fmt("Cannot replay height %d. WAL does not contain #ENDHEIGHT for %d.", csHeight, csHeight-1))
 	}
-	defer gr.Close()
 
 	log.Notice("Catchup by replaying consensus messages", "height", csHeight)
 
@@ -147,7 +171,7 @@ func (cs *ConsensusState) catchupReplay(csHeight int) error {
 //--------------------------------------------------------------------------------
 
 // Parses marker lines of the form:
-// #HEIGHT: 12345
+// #ENDHEIGHT: 12345
 func makeHeightSearchFunc(height int) auto.SearchFunc {
 	return func(line string) (int, error) {
 		line = strings.TrimRight(line, "\n")
@@ -273,15 +297,18 @@ func (h *Handshaker) ReplayBlocks(appHash []byte, appBlockHeight int, proxyApp p
 
 		} else if appBlockHeight == stateBlockHeight {
 			// We haven't run Commit (both the state and app are one block behind),
-			// so run through consensus with the real app
+			// so replayBlock with the real app.
+			// NOTE: We could instead use the cs.WAL on cs.Start,
+			// but we'd have to allow the WAL to replay a block that wrote it's ENDHEIGHT
 			log.Info("Replay last block using real app")
-			return h.replayLastBlock(proxyApp.Consensus())
+			return h.replayBlock(storeBlockHeight, proxyApp.Consensus())
 
 		} else if appBlockHeight == storeBlockHeight {
-			// We ran Commit, but didn't save the state, so run through consensus with mock app
-			mockApp := newMockProxyApp(appHash)
+			// We ran Commit, but didn't save the state, so replayBlock with mock app
+			abciResponses := h.state.LoadABCIResponses()
+			mockApp := newMockProxyApp(appHash, abciResponses)
 			log.Info("Replay last block using mock app")
-			return h.replayLastBlock(mockApp)
+			return h.replayBlock(storeBlockHeight, mockApp)
 		}
 
 	}
@@ -290,24 +317,23 @@ func (h *Handshaker) ReplayBlocks(appHash []byte, appBlockHeight int, proxyApp p
 	return nil, nil
 }
 
-func (h *Handshaker) replayBlocks(proxyApp proxy.AppConns, appBlockHeight, storeBlockHeight int, useReplayFunc bool) ([]byte, error) {
+func (h *Handshaker) replayBlocks(proxyApp proxy.AppConns, appBlockHeight, storeBlockHeight int, mutateState bool) ([]byte, error) {
 	// App is further behind than it should be, so we need to replay blocks.
 	// We replay all blocks from appBlockHeight+1.
-	// If useReplayFunc == true, stop short of the last block
-	// so it can be replayed using the WAL in ReplayBlocks.
 	// Note that we don't have an old version of the state,
-	// so we by-pass state validation using sm.ApplyBlock.
+	// so we by-pass state validation/mutation using sm.ExecCommitBlock.
+	// If mutateState == true, the final block is replayed with h.replayBlock()
 
 	var appHash []byte
 	var err error
 	finalBlock := storeBlockHeight
-	if useReplayFunc {
+	if mutateState {
 		finalBlock -= 1
 	}
 	for i := appBlockHeight + 1; i <= finalBlock; i++ {
 		log.Info("Applying block", "height", i)
 		block := h.store.LoadBlock(i)
-		appHash, err = sm.ApplyBlock(proxyApp.Consensus(), block)
+		appHash, err = sm.ExecCommitBlock(proxyApp.Consensus(), block)
 		if err != nil {
 			return nil, err
 		}
@@ -315,44 +341,29 @@ func (h *Handshaker) replayBlocks(proxyApp proxy.AppConns, appBlockHeight, store
 		h.nBlocks += 1
 	}
 
-	if useReplayFunc {
+	if mutateState {
 		// sync the final block
-		return h.ReplayBlocks(appHash, finalBlock, proxyApp)
+		return h.replayBlock(storeBlockHeight, proxyApp.Consensus())
 	}
 
 	return appHash, h.checkAppHash(appHash)
 }
 
-// Replay the last block through the consensus and return the AppHash from after Commit.
-func (h *Handshaker) replayLastBlock(proxyApp proxy.AppConnConsensus) ([]byte, error) {
+// ApplyBlock on the proxyApp with the last block.
+func (h *Handshaker) replayBlock(height int, proxyApp proxy.AppConnConsensus) ([]byte, error) {
 	mempool := types.MockMempool{}
-	cs := NewConsensusState(h.config, h.state, proxyApp, h.store, mempool)
 
-	evsw := types.NewEventSwitch()
-	evsw.Start()
-	defer evsw.Stop()
-	cs.SetEventSwitch(evsw)
-	newBlockCh := subscribeToEvent(evsw, "consensus-replay", types.EventStringNewBlock(), 1)
+	var eventCache types.Fireable // nil
+	block := h.store.LoadBlock(height)
+	meta := h.store.LoadBlockMeta(height)
 
-	// run through the WAL, commit new block, stop
-	if _, err := cs.Start(); err != nil {
+	if err := h.state.ApplyBlock(eventCache, proxyApp, block, meta.BlockID.PartsHeader, mempool); err != nil {
 		return nil, err
 	}
-	defer cs.Stop()
-
-	timeout := h.config.GetInt("timeout_handshake")
-	timer := time.NewTimer(time.Duration(timeout) * time.Millisecond)
-	log.Notice("Attempting to replay last block", "height", h.store.Height(), "timeout", timeout)
-
-	select {
-	case <-newBlockCh:
-	case <-timer.C:
-		return nil, ErrReplayLastBlockTimeout
-	}
 
 	h.nBlocks += 1
 
-	return cs.state.AppHash, nil
+	return h.state.AppHash, nil
 }
 
 func (h *Handshaker) checkAppHash(appHash []byte) error {
@@ -364,9 +375,14 @@ func (h *Handshaker) checkAppHash(appHash []byte) error {
 }
 
 //--------------------------------------------------------------------------------
-
-func newMockProxyApp(appHash []byte) proxy.AppConnConsensus {
-	clientCreator := proxy.NewLocalClientCreator(&mockProxyApp{appHash: appHash})
+// mockProxyApp uses ABCIResponses to give the right results
+// Useful because we don't want to call Commit() twice for the same block on the real app.
+
+func newMockProxyApp(appHash []byte, abciResponses *sm.ABCIResponses) proxy.AppConnConsensus {
+	clientCreator := proxy.NewLocalClientCreator(&mockProxyApp{
+		appHash:       appHash,
+		abciResponses: abciResponses,
+	})
 	cli, _ := clientCreator.NewABCIClient()
 	return proxy.NewAppConnConsensus(cli)
 }
@@ -374,7 +390,24 @@ func newMockProxyApp(appHash []byte) proxy.AppConnConsensus {
 type mockProxyApp struct {
 	abci.BaseApplication
 
-	appHash []byte
+	appHash       []byte
+	txCount       int
+	abciResponses *sm.ABCIResponses
+}
+
+func (mock *mockProxyApp) DeliverTx(tx []byte) abci.Result {
+	r := mock.abciResponses.DeliverTx[mock.txCount]
+	mock.txCount += 1
+	return abci.Result{
+		r.Code,
+		r.Data,
+		r.Log,
+	}
+}
+
+func (mock *mockProxyApp) EndBlock(height uint64) abci.ResponseEndBlock {
+	mock.txCount = 0
+	return mock.abciResponses.EndBlock
 }
 
 func (mock *mockProxyApp) Commit() abci.Result {
diff --git a/consensus/replay_test.go b/consensus/replay_test.go
index c70b60fa0..43204ab72 100644
--- a/consensus/replay_test.go
+++ b/consensus/replay_test.go
@@ -443,7 +443,7 @@ func buildTMStateFromChain(config cfg.Config, state *sm.State, chain []*types.Bl
 
 func makeBlockchainFromWAL(wal *WAL) ([]*types.Block, []*types.Commit, error) {
 	// Search for height marker
-	gr, found, err := wal.group.Search("#HEIGHT: ", makeHeightSearchFunc(1))
+	gr, found, err := wal.group.Search("#ENDHEIGHT: ", makeHeightSearchFunc(0))
 	if err != nil {
 		return nil, nil, err
 	}
diff --git a/consensus/state.go b/consensus/state.go
index d69435814..6ff97ddc8 100644
--- a/consensus/state.go
+++ b/consensus/state.go
@@ -1216,13 +1216,26 @@ func (cs *ConsensusState) finalizeCommit(height int) {
 
 	fail.Fail() // XXX
 
+	// Finish writing to the WAL for this height.
+	// NOTE: If we fail before writing this, we'll never write it,
+	// and just recover by running ApplyBlock in the Handshake.
+	// If we moved it before persisting the block, we'd have to allow
+	// WAL replay for blocks with an #ENDHEIGHT
+	// As is, ConsensusState should not be started again
+	// until we successfully call ApplyBlock (ie. here or in Handshake after restart)
+	if cs.wal != nil {
+		cs.wal.writeEndHeight(height)
+	}
+
+	fail.Fail() // XXX
+
 	// Create a copy of the state for staging
 	// and an event cache for txs
 	stateCopy := cs.state.Copy()
 	eventCache := types.NewEventCache(cs.evsw)
 
-	// Execute and commit the block, and update the mempool.
-	// All calls to the proxyAppConn should come here.
+	// Execute and commit the block, update and save the state, and update the mempool.
+	// All calls to the proxyAppConn come here.
 	// NOTE: the block.AppHash wont reflect these txs until the next block
 	err := stateCopy.ApplyBlock(eventCache, cs.proxyAppConn, block, blockParts.Header(), cs.mempool)
 	if err != nil {
@@ -1232,20 +1245,24 @@ func (cs *ConsensusState) finalizeCommit(height int) {
 
 	fail.Fail() // XXX
 
-	// Fire off event for new block.
-	// TODO: Handle app failure.  See #177
+	// Fire event for new block.
+	// NOTE: If we fail before firing, these events will never fire
+	//
+	// TODO: Either
+	// 	* Fire before persisting state, in ApplyBlock
+	//	* Fire on start up if we haven't written any new WAL msgs
+	//   Both options mean we may fire more than once. Is that fine ?
 	types.FireEventNewBlock(cs.evsw, types.EventDataNewBlock{block})
 	types.FireEventNewBlockHeader(cs.evsw, types.EventDataNewBlockHeader{block.Header})
 	eventCache.Flush()
 
-	// Save the state.
-	stateCopy.Save()
-
 	fail.Fail() // XXX
 
 	// NewHeightStep!
 	cs.updateToState(stateCopy)
 
+	fail.Fail() // XXX
+
 	// cs.StartTime is already set.
 	// Schedule Round0 to start soon.
 	cs.scheduleRound0(&cs.RoundState)
diff --git a/consensus/test_data/build.sh b/consensus/test_data/build.sh
index ea0c9604a..2759c0e38 100644
--- a/consensus/test_data/build.sh
+++ b/consensus/test_data/build.sh
@@ -27,7 +27,7 @@ killall tendermint
 # /q would print up to and including the match, then quit. 
 # /Q doesn't include the match. 
 # http://unix.stackexchange.com/questions/11305/grep-show-all-the-file-up-to-the-match
-sed '/HEIGHT: 2/Q' ~/.tendermint/data/cs.wal/wal  > consensus/test_data/empty_block.cswal
+sed '/ENDHEIGHT: 1/Q' ~/.tendermint/data/cs.wal/wal  > consensus/test_data/empty_block.cswal
 
 reset
 }
@@ -41,7 +41,7 @@ sleep 7
 killall tendermint
 kill -9 $PID
 
-sed '/HEIGHT: 7/Q' ~/.tendermint/data/cs.wal/wal  > consensus/test_data/many_blocks.cswal
+sed '/ENDHEIGHT: 6/Q' ~/.tendermint/data/cs.wal/wal  > consensus/test_data/many_blocks.cswal
 
 reset
 }
@@ -56,7 +56,7 @@ sleep 10
 killall tendermint
 kill -9 $PID
 
-sed '/HEIGHT: 2/Q' ~/.tendermint/data/cs.wal/wal  > consensus/test_data/small_block1.cswal
+sed '/ENDHEIGHT: 1/Q' ~/.tendermint/data/cs.wal/wal  > consensus/test_data/small_block1.cswal
 
 reset
 }
@@ -73,7 +73,7 @@ sleep 5
 killall tendermint
 kill -9 $PID
 
-sed '/HEIGHT: 2/Q' ~/.tendermint/data/cs.wal/wal  > consensus/test_data/small_block2.cswal
+sed '/ENDHEIGHT: 1/Q' ~/.tendermint/data/cs.wal/wal  > consensus/test_data/small_block2.cswal
 
 reset
 }
diff --git a/consensus/test_data/empty_block.cswal b/consensus/test_data/empty_block.cswal
index a3a3585ce..aa5b232c9 100644
--- a/consensus/test_data/empty_block.cswal
+++ b/consensus/test_data/empty_block.cswal
@@ -1,4 +1,4 @@
-#HEIGHT: 1
+#ENDHEIGHT: 0
 {"time":"2016-12-18T05:05:33.502Z","msg":[3,{"duration":974084551,"height":1,"round":0,"step":1}]}
 {"time":"2016-12-18T05:05:33.505Z","msg":[1,{"height":1,"round":0,"step":"RoundStepPropose"}]}
 {"time":"2016-12-18T05:05:33.505Z","msg":[2,{"msg":[17,{"Proposal":{"height":1,"round":0,"block_parts_header":{"total":1,"hash":"71D2DA2336A9F84C22A28FF6C67F35F3478FC0AF"},"pol_round":-1,"pol_block_id":{"hash":"","parts":{"total":0,"hash":""}},"signature":[1,"62C0F2BCCB491399EEDAF8E85837ADDD4E25BAB7A84BFC4F0E88594531FBC6D4755DEC7E6427F04AD7EB8BB89502762AB4380C7BBA93A4C297E6180EC78E3504"]}}],"peer_key":""}]}
diff --git a/consensus/test_data/many_blocks.cswal b/consensus/test_data/many_blocks.cswal
index 9ef06c32c..fd103cb1e 100644
--- a/consensus/test_data/many_blocks.cswal
+++ b/consensus/test_data/many_blocks.cswal
@@ -1,4 +1,4 @@
-#HEIGHT: 1
+#ENDHEIGHT: 0
 {"time":"2017-02-17T23:54:19.013Z","msg":[3,{"duration":969121813,"height":1,"round":0,"step":1}]}
 {"time":"2017-02-17T23:54:19.014Z","msg":[1,{"height":1,"round":0,"step":"RoundStepPropose"}]}
 {"time":"2017-02-17T23:54:19.014Z","msg":[2,{"msg":[17,{"Proposal":{"height":1,"round":0,"block_parts_header":{"total":1,"hash":"2E32C8D500E936D27A47FCE3FF4BE7C1AFB3FAE1"},"pol_round":-1,"pol_block_id":{"hash":"","parts":{"total":0,"hash":""}},"signature":[1,"105A5A834E9AE2FA2191CAB5CB20D63594BA7859BD3EB92F055C8A35476D71F0D89F9FD5B0FF030D021533C71A81BF6E8F026BF4A37FC637CF38CA35291A9D00"]}}],"peer_key":""}]}
@@ -8,7 +8,7 @@
 {"time":"2017-02-17T23:54:19.016Z","msg":[1,{"height":1,"round":0,"step":"RoundStepPrecommit"}]}
 {"time":"2017-02-17T23:54:19.016Z","msg":[2,{"msg":[20,{"Vote":{"validator_address":"D028C9981F7A87F3093672BF0D5B0E2A1B3ED456","validator_index":0,"height":1,"round":0,"type":2,"block_id":{"hash":"3F32EE37F9EA674A2173CAD651836A8EE628B5C7","parts":{"total":1,"hash":"2E32C8D500E936D27A47FCE3FF4BE7C1AFB3FAE1"}},"signature":[1,"2B1070A5AB9305612A3AE74A8036D82B5E49E0DBBFBC7D723DB985CC8A8E72A52FF8E34D85273FEB8B901945CA541FA5142C3C4D43A04E9205ACECF53FD19B01"]}}],"peer_key":""}]}
 {"time":"2017-02-17T23:54:19.017Z","msg":[1,{"height":1,"round":0,"step":"RoundStepCommit"}]}
-#HEIGHT: 2
+#ENDHEIGHT: 1
 {"time":"2017-02-17T23:54:19.019Z","msg":[1,{"height":2,"round":0,"step":"RoundStepNewHeight"}]}
 {"time":"2017-02-17T23:54:20.017Z","msg":[3,{"duration":998073370,"height":2,"round":0,"step":1}]}
 {"time":"2017-02-17T23:54:20.018Z","msg":[1,{"height":2,"round":0,"step":"RoundStepPropose"}]}
@@ -19,7 +19,7 @@
 {"time":"2017-02-17T23:54:20.021Z","msg":[1,{"height":2,"round":0,"step":"RoundStepPrecommit"}]}
 {"time":"2017-02-17T23:54:20.021Z","msg":[2,{"msg":[20,{"Vote":{"validator_address":"D028C9981F7A87F3093672BF0D5B0E2A1B3ED456","validator_index":0,"height":2,"round":0,"type":2,"block_id":{"hash":"32310D174A99844713693C9815D2CA660364E028","parts":{"total":1,"hash":"D008E9014CDDEA8EC95E1E99E21333241BD52DFC"}},"signature":[1,"AA9F03D0707752301D7CBFCF4F0BCDBD666A46C1CAED3910BD64A3C5C2874AAF328172646C951C5E2FD962359C382A3CBBA2C73EC9B533668C6386995B83EC08"]}}],"peer_key":""}]}
 {"time":"2017-02-17T23:54:20.022Z","msg":[1,{"height":2,"round":0,"step":"RoundStepCommit"}]}
-#HEIGHT: 3
+#ENDHEIGHT: 2
 {"time":"2017-02-17T23:54:20.025Z","msg":[1,{"height":3,"round":0,"step":"RoundStepNewHeight"}]}
 {"time":"2017-02-17T23:54:21.022Z","msg":[3,{"duration":997103974,"height":3,"round":0,"step":1}]}
 {"time":"2017-02-17T23:54:21.024Z","msg":[1,{"height":3,"round":0,"step":"RoundStepPropose"}]}
@@ -30,7 +30,7 @@
 {"time":"2017-02-17T23:54:21.028Z","msg":[1,{"height":3,"round":0,"step":"RoundStepPrecommit"}]}
 {"time":"2017-02-17T23:54:21.028Z","msg":[2,{"msg":[20,{"Vote":{"validator_address":"D028C9981F7A87F3093672BF0D5B0E2A1B3ED456","validator_index":0,"height":3,"round":0,"type":2,"block_id":{"hash":"37AF6866DA8C3167CFC280FAE47B6ED441B00D5B","parts":{"total":1,"hash":"2E5DE5777A5AD899CD2531304F42A470509DE989"}},"signature":[1,"C900519E305EC03392E7D197D5FAB535DB240C9C0BA5375A1679C75BAAA07C7410C0EF43CF97D98F2C08A1D739667D5ACFF6233A1FAE75D3DA275AEA422EFD0F"]}}],"peer_key":""}]}
 {"time":"2017-02-17T23:54:21.028Z","msg":[1,{"height":3,"round":0,"step":"RoundStepCommit"}]}
-#HEIGHT: 4
+#ENDHEIGHT: 3
 {"time":"2017-02-17T23:54:21.032Z","msg":[1,{"height":4,"round":0,"step":"RoundStepNewHeight"}]}
 {"time":"2017-02-17T23:54:22.028Z","msg":[3,{"duration":996302067,"height":4,"round":0,"step":1}]}
 {"time":"2017-02-17T23:54:22.030Z","msg":[1,{"height":4,"round":0,"step":"RoundStepPropose"}]}
@@ -41,7 +41,7 @@
 {"time":"2017-02-17T23:54:22.033Z","msg":[1,{"height":4,"round":0,"step":"RoundStepPrecommit"}]}
 {"time":"2017-02-17T23:54:22.033Z","msg":[2,{"msg":[20,{"Vote":{"validator_address":"D028C9981F7A87F3093672BF0D5B0E2A1B3ED456","validator_index":0,"height":4,"round":0,"type":2,"block_id":{"hash":"04715E223BF4327FFA9B0D5AD849B74A099D5DEC","parts":{"total":1,"hash":"24CEBCBEB833F56D47AD14354071B3B7A243068A"}},"signature":[1,"F544743F17479A61F94B0F68C63D254BD60493D78E818D48A5859133619AEE5E92C47CAD89C654DF64E0911C3152091E047555D5F14655D95B9681AE9B336505"]}}],"peer_key":""}]}
 {"time":"2017-02-17T23:54:22.034Z","msg":[1,{"height":4,"round":0,"step":"RoundStepCommit"}]}
-#HEIGHT: 5
+#ENDHEIGHT: 4
 {"time":"2017-02-17T23:54:22.036Z","msg":[1,{"height":5,"round":0,"step":"RoundStepNewHeight"}]}
 {"time":"2017-02-17T23:54:23.034Z","msg":[3,{"duration":997096276,"height":5,"round":0,"step":1}]}
 {"time":"2017-02-17T23:54:23.035Z","msg":[1,{"height":5,"round":0,"step":"RoundStepPropose"}]}
@@ -52,7 +52,7 @@
 {"time":"2017-02-17T23:54:23.038Z","msg":[1,{"height":5,"round":0,"step":"RoundStepPrecommit"}]}
 {"time":"2017-02-17T23:54:23.038Z","msg":[2,{"msg":[20,{"Vote":{"validator_address":"D028C9981F7A87F3093672BF0D5B0E2A1B3ED456","validator_index":0,"height":5,"round":0,"type":2,"block_id":{"hash":"FDC6D837995BEBBBFCBF3E7D7CF44F8FDA448543","parts":{"total":1,"hash":"A52BAA9C2E52E633A1605F4B930205613E3E7A2F"}},"signature":[1,"DF51D23D5D2C57598F67791D953A6C2D9FC5865A3048ADA4469B37500D2996B95732E0DC6F99EAEAEA12B4818CE355C7B701D16857D2AC767D740C2E30E9260C"]}}],"peer_key":""}]}
 {"time":"2017-02-17T23:54:23.038Z","msg":[1,{"height":5,"round":0,"step":"RoundStepCommit"}]}
-#HEIGHT: 6
+#ENDHEIGHT: 5
 {"time":"2017-02-17T23:54:23.041Z","msg":[1,{"height":6,"round":0,"step":"RoundStepNewHeight"}]}
 {"time":"2017-02-17T23:54:24.038Z","msg":[3,{"duration":997341910,"height":6,"round":0,"step":1}]}
 {"time":"2017-02-17T23:54:24.040Z","msg":[1,{"height":6,"round":0,"step":"RoundStepPropose"}]}
diff --git a/consensus/test_data/small_block1.cswal b/consensus/test_data/small_block1.cswal
index 90103dff3..d4eff73f1 100644
--- a/consensus/test_data/small_block1.cswal
+++ b/consensus/test_data/small_block1.cswal
@@ -1,4 +1,4 @@
-#HEIGHT: 1
+#ENDHEIGHT: 0
 {"time":"2016-12-18T05:05:38.593Z","msg":[3,{"duration":970717663,"height":1,"round":0,"step":1}]}
 {"time":"2016-12-18T05:05:38.595Z","msg":[1,{"height":1,"round":0,"step":"RoundStepPropose"}]}
 {"time":"2016-12-18T05:05:38.595Z","msg":[2,{"msg":[17,{"Proposal":{"height":1,"round":0,"block_parts_header":{"total":1,"hash":"A434EC796DF1CECC01296E953839C4675863A4E5"},"pol_round":-1,"pol_block_id":{"hash":"","parts":{"total":0,"hash":""}},"signature":[1,"39563C3C7EDD9855B2971457A5DABF05CFDAF52805658847EB1F05115B8341344A77761CC85E670AF1B679DA9FC0905231957174699FE8326DBE7706209BDD0B"]}}],"peer_key":""}]}
diff --git a/consensus/test_data/small_block2.cswal b/consensus/test_data/small_block2.cswal
index 1be6c4c93..b5d1d282b 100644
--- a/consensus/test_data/small_block2.cswal
+++ b/consensus/test_data/small_block2.cswal
@@ -1,4 +1,4 @@
-#HEIGHT: 1
+#ENDHEIGHT: 0
 {"time":"2016-12-18T05:05:43.641Z","msg":[3,{"duration":969409681,"height":1,"round":0,"step":1}]}
 {"time":"2016-12-18T05:05:43.643Z","msg":[1,{"height":1,"round":0,"step":"RoundStepPropose"}]}
 {"time":"2016-12-18T05:05:43.643Z","msg":[2,{"msg":[17,{"Proposal":{"height":1,"round":0,"block_parts_header":{"total":5,"hash":"C916905C3C444501DDDAA1BF52E959B7531E762E"},"pol_round":-1,"pol_block_id":{"hash":"","parts":{"total":0,"hash":""}},"signature":[1,"F1A8E9928889C68FD393F3983B5362AECA4A95AA13FE3C78569B2515EC046893CB718071CAF54F3F1507DCD851B37CD5557EA17BB5471D2DC6FB5AC5FBB72E02"]}}],"peer_key":""}]}
diff --git a/consensus/wal.go b/consensus/wal.go
index 6d8eb3819..a89eff5e4 100644
--- a/consensus/wal.go
+++ b/consensus/wal.go
@@ -59,7 +59,7 @@ func (wal *WAL) OnStart() error {
 	if err != nil {
 		return err
 	} else if size == 0 {
-		wal.writeHeight(1)
+		wal.writeEndHeight(0)
 	}
 	_, err = wal.group.Start()
 	return err
@@ -83,12 +83,6 @@ func (wal *WAL) Save(wmsg WALMessage) {
 			}
 		}
 	}
-	// Write #HEIGHT: XYZ if new height
-	if edrs, ok := wmsg.(types.EventDataRoundState); ok {
-		if edrs.Step == RoundStepNewHeight.String() {
-			wal.writeHeight(edrs.Height)
-		}
-	}
 	// Write the wal message
 	var wmsgBytes = wire.JSONBytes(TimedWALMessage{time.Now(), wmsg})
 	err := wal.group.WriteLine(string(wmsgBytes))
@@ -101,8 +95,8 @@ func (wal *WAL) Save(wmsg WALMessage) {
 	}
 }
 
-func (wal *WAL) writeHeight(height int) {
-	wal.group.WriteLine(Fmt("#HEIGHT: %v", height))
+func (wal *WAL) writeEndHeight(height int) {
+	wal.group.WriteLine(Fmt("#ENDHEIGHT: %v", height))
 
 	// TODO: only flush when necessary
 	if err := wal.group.Flush(); err != nil {
diff --git a/glide.lock b/glide.lock
index 63b3875d0..f0ede402e 100644
--- a/glide.lock
+++ b/glide.lock
@@ -1,5 +1,5 @@
 hash: d9724aa287c40d1b3856b6565f09235d809c8b2f7c6537c04f597137c0d6cd26
-updated: 2017-04-11T15:24:16.619608243-04:00
+updated: 2017-04-14T17:17:31.933202871-04:00
 imports:
 - name: github.com/btcsuite/btcd
   version: b8df516b4b267acf2de46be593a9d948d1d2c420
@@ -85,7 +85,7 @@ imports:
 - name: github.com/tendermint/go-clist
   version: 3baa390bbaf7634251c42ad69a8682e7e3990552
 - name: github.com/tendermint/go-common
-  version: 6af2364fa91ef2f3afc8ba0db33b66d9d3ae006c
+  version: 714fdaee3bb3f8670e721a75c5ddda8787b256dd
   subpackages:
   - test
 - name: github.com/tendermint/go-config
@@ -111,13 +111,13 @@ imports:
   subpackages:
   - upnp
 - name: github.com/tendermint/go-rpc
-  version: 9d18cbe74e66f875afa36d2fa3be280e4a2dc9e6
+  version: 4671c44b2d124f7f6f6243dbfbf4ae2bf42ee809
   subpackages:
   - client
   - server
   - types
 - name: github.com/tendermint/go-wire
-  version: 09dae074245a8042aa689d084af774e6ad6a90bb
+  version: 50889e2b4a9ba65b67be86a486f25853d514b937
 - name: github.com/tendermint/log15
   version: ae0f3d6450da9eac7074b439c8e1c3cabf0d5ce6
   subpackages:
@@ -166,12 +166,4 @@ imports:
   - stats
   - tap
   - transport
-testImports:
-- name: github.com/davecgh/go-spew
-  version: 6d212800a42e8ab5c146b8ace3490ee17e5225f9
-  subpackages:
-  - spew
-- name: github.com/pmezard/go-difflib
-  version: d8ed2627bdf02c080bf22230dbb337003b7aba2d
-  subpackages:
-  - difflib
+testImports: []
diff --git a/state/execution.go b/state/execution.go
index 25d5dcd3a..0b1aff699 100644
--- a/state/execution.go
+++ b/state/execution.go
@@ -13,58 +13,37 @@ import (
 	"github.com/tendermint/tendermint/types"
 )
 
-// ExecBlock executes the block to mutate State.
+//--------------------------------------------------
+// Execute the block
+
+// ValExecBlock executes the block, but does NOT mutate State.
 // + validates the block
 // + executes block.Txs on the proxyAppConn
-// + updates validator sets
-// + returns block.Txs results
-func (s *State) ExecBlock(eventCache types.Fireable, proxyAppConn proxy.AppConnConsensus, block *types.Block, blockPartsHeader types.PartSetHeader) ([]*types.TxResult, error) {
+func (s *State) ValExecBlock(eventCache types.Fireable, proxyAppConn proxy.AppConnConsensus, block *types.Block) (*ABCIResponses, error) {
 	// Validate the block.
 	if err := s.validateBlock(block); err != nil {
 		return nil, ErrInvalidBlock(err)
 	}
 
-	// compute bitarray of validators that signed
-	signed := commitBitArrayFromBlock(block)
-	_ = signed // TODO send on begin block
-
-	// copy the valset
-	valSet := s.Validators.Copy()
-	nextValSet := valSet.Copy()
-
 	// Execute the block txs
-	txResults, changedValidators, err := execBlockOnProxyApp(eventCache, proxyAppConn, block)
+	abciResponses, err := execBlockOnProxyApp(eventCache, proxyAppConn, block)
 	if err != nil {
 		// There was some error in proxyApp
 		// TODO Report error and wait for proxyApp to be available.
 		return nil, ErrProxyAppConn(err)
 	}
 
-	// update the validator set
-	err = updateValidators(nextValSet, changedValidators)
-	if err != nil {
-		log.Warn("Error changing validator set", "error", err)
-		// TODO: err or carry on?
-	}
-
-	// All good!
-	// Update validator accums and set state variables
-	nextValSet.IncrementAccum(1)
-	s.SetBlockAndValidators(block.Header, blockPartsHeader, valSet, nextValSet)
-
-	fail.Fail() // XXX
-
-	return txResults, nil
+	return abciResponses, nil
 }
 
 // Executes block's transactions on proxyAppConn.
 // Returns a list of transaction results and updates to the validator set
 // TODO: Generate a bitmap or otherwise store tx validity in state.
-func execBlockOnProxyApp(eventCache types.Fireable, proxyAppConn proxy.AppConnConsensus, block *types.Block) ([]*types.TxResult, []*abci.Validator, error) {
+func execBlockOnProxyApp(eventCache types.Fireable, proxyAppConn proxy.AppConnConsensus, block *types.Block) (*ABCIResponses, error) {
 	var validTxs, invalidTxs = 0, 0
 
-	txResults := make([]*types.TxResult, len(block.Txs))
 	txIndex := 0
+	abciResponses := NewABCIResponses(block)
 
 	// Execute transactions and get hash
 	proxyCb := func(req *abci.Request, res *abci.Response) {
@@ -84,12 +63,7 @@ func execBlockOnProxyApp(eventCache types.Fireable, proxyAppConn proxy.AppConnCo
 				txError = txResult.Code.String()
 			}
 
-			txResults[txIndex] = &types.TxResult{
-				Height: uint64(block.Height),
-				Index:  uint32(txIndex),
-				Tx:     req.GetDeliverTx().Tx,
-				Result: *txResult,
-			}
+			abciResponses.DeliverTx[txIndex] = txResult
 			txIndex++
 
 			// NOTE: if we count we can access the tx from the block instead of
@@ -111,36 +85,32 @@ func execBlockOnProxyApp(eventCache types.Fireable, proxyAppConn proxy.AppConnCo
 	err := proxyAppConn.BeginBlockSync(block.Hash(), types.TM2PB.Header(block.Header))
 	if err != nil {
 		log.Warn("Error in proxyAppConn.BeginBlock", "error", err)
-		return nil, nil, err
+		return nil, err
 	}
 
-	fail.Fail() // XXX
-
 	// Run txs of block
 	for _, tx := range block.Txs {
-		fail.FailRand(len(block.Txs)) // XXX
 		proxyAppConn.DeliverTxAsync(tx)
 		if err := proxyAppConn.Error(); err != nil {
-			return nil, nil, err
+			return nil, err
 		}
 	}
 
-	fail.Fail() // XXX
-
 	// End block
-	respEndBlock, err := proxyAppConn.EndBlockSync(uint64(block.Height))
+	abciResponses.EndBlock, err = proxyAppConn.EndBlockSync(uint64(block.Height))
 	if err != nil {
 		log.Warn("Error in proxyAppConn.EndBlock", "error", err)
-		return nil, nil, err
+		return nil, err
 	}
 
-	fail.Fail() // XXX
+	valDiff := abciResponses.EndBlock.Diffs
 
 	log.Info("Executed block", "height", block.Height, "valid txs", validTxs, "invalid txs", invalidTxs)
-	if len(respEndBlock.Diffs) > 0 {
-		log.Info("Update to validator set", "updates", abci.ValidatorsString(respEndBlock.Diffs))
+	if len(valDiff) > 0 {
+		log.Info("Update to validator set", "updates", abci.ValidatorsString(valDiff))
 	}
-	return txResults, respEndBlock.Diffs, nil
+
+	return abciResponses, nil
 }
 
 func updateValidators(validators *types.ValidatorSet, changedValidators []*abci.Validator) error {
@@ -230,27 +200,43 @@ func (s *State) validateBlock(block *types.Block) error {
 	return nil
 }
 
-// ApplyBlock executes the block, then commits and updates the mempool
-// atomically, optionally indexing transaction results.
+//-----------------------------------------------------------------------------
+// ApplyBlock validates & executes the block, updates state w/ ABCI responses,
+// then commits and updates the mempool atomically, then saves state.
+// Transaction results are optionally indexed.
+
+// Validate, execute, and commit block against app, save block and state
 func (s *State) ApplyBlock(eventCache types.Fireable, proxyAppConn proxy.AppConnConsensus,
 	block *types.Block, partsHeader types.PartSetHeader, mempool types.Mempool) error {
 
-	txResults, err := s.ExecBlock(eventCache, proxyAppConn, block, partsHeader)
+	abciResponses, err := s.ValExecBlock(eventCache, proxyAppConn, block)
 	if err != nil {
 		return fmt.Errorf("Exec failed for application: %v", err)
 	}
 
+	fail.Fail() // XXX
+
+	// index txs. This could run in the background
+	s.indexTxs(abciResponses)
+
+	// save the results before we commit
+	s.SaveABCIResponses(abciResponses)
+
+	fail.Fail() // XXX
+
+	// now update the block and validators
+	s.SetBlockAndValidators(block.Header, partsHeader, abciResponses)
+
 	// lock mempool, commit state, update mempoool
 	err = s.CommitStateUpdateMempool(proxyAppConn, block, mempool)
 	if err != nil {
 		return fmt.Errorf("Commit failed for application: %v", err)
 	}
 
-	batch := txindex.NewBatch(block.NumTxs)
-	for _, r := range txResults {
-		batch.Add(*r)
-	}
-	s.TxIndexer.AddBatch(batch)
+	fail.Fail() // XXX
+
+	// save the state
+	s.Save()
 
 	return nil
 }
@@ -282,11 +268,27 @@ func (s *State) CommitStateUpdateMempool(proxyAppConn proxy.AppConnConsensus, bl
 	return nil
 }
 
-// Apply and commit a block, but without all the state validation.
+func (s *State) indexTxs(abciResponses *ABCIResponses) {
+	// save the tx results using the TxIndexer
+	// NOTE: these may be overwriting, but the values should be the same.
+	batch := txindex.NewBatch(len(abciResponses.DeliverTx))
+	for i, d := range abciResponses.DeliverTx {
+		tx := abciResponses.txs[i]
+		batch.Add(types.TxResult{
+			Height: uint64(abciResponses.Height),
+			Index:  uint32(i),
+			Tx:     tx,
+			Result: *d,
+		})
+	}
+	s.TxIndexer.AddBatch(batch)
+}
+
+// Exec and commit a block on the proxyApp without validating or mutating the state
 // Returns the application root hash (result of abci.Commit)
-func ApplyBlock(appConnConsensus proxy.AppConnConsensus, block *types.Block) ([]byte, error) {
+func ExecCommitBlock(appConnConsensus proxy.AppConnConsensus, block *types.Block) ([]byte, error) {
 	var eventCache types.Fireable // nil
-	_, _, err := execBlockOnProxyApp(eventCache, appConnConsensus, block)
+	_, err := execBlockOnProxyApp(eventCache, appConnConsensus, block)
 	if err != nil {
 		log.Warn("Error executing block on proxy app", "height", block.Height, "err", err)
 		return nil, err
diff --git a/state/state.go b/state/state.go
index 14b324d5f..086b0e710 100644
--- a/state/state.go
+++ b/state/state.go
@@ -6,6 +6,7 @@ import (
 	"sync"
 	"time"
 
+	abci "github.com/tendermint/abci/types"
 	. "github.com/tendermint/go-common"
 	cfg "github.com/tendermint/go-config"
 	dbm "github.com/tendermint/go-db"
@@ -16,7 +17,8 @@ import (
 )
 
 var (
-	stateKey = []byte("stateKey")
+	stateKey         = []byte("stateKey")
+	abciResponsesKey = []byte("abciResponsesKey")
 )
 
 //-----------------------------------------------------------------------------
@@ -31,7 +33,7 @@ type State struct {
 	GenesisDoc *types.GenesisDoc
 	ChainID    string
 
-	// updated at end of ExecBlock
+	// updated at end of SetBlockAndValidators
 	LastBlockHeight int // Genesis state has this set to 0.  So, Block(H=0) does not exist.
 	LastBlockID     types.BlockID
 	LastBlockTime   time.Time
@@ -42,6 +44,10 @@ type State struct {
 	AppHash []byte
 
 	TxIndexer txindex.TxIndexer `json:"-"` // Transaction indexer.
+
+	// Intermediate results from processing
+	// Persisted separately from the state
+	abciResponses *ABCIResponses
 }
 
 func LoadState(db dbm.DB) *State {
@@ -58,7 +64,7 @@ func loadState(db dbm.DB, key []byte) *State {
 		wire.ReadBinaryPtr(&s, r, 0, n, err)
 		if *err != nil {
 			// DATA HAS BEEN CORRUPTED OR THE SPEC HAS CHANGED
-			Exit(Fmt("Data has been corrupted or its spec has changed: %v\n", *err))
+			Exit(Fmt("LoadState: Data has been corrupted or its spec has changed: %v\n", *err))
 		}
 		// TODO: ensure that buf is completely read.
 	}
@@ -86,6 +92,29 @@ func (s *State) Save() {
 	s.db.SetSync(stateKey, s.Bytes())
 }
 
+// Sets the ABCIResponses in the state and writes them to disk
+// in case we crash after app.Commit and before s.Save()
+func (s *State) SaveABCIResponses(abciResponses *ABCIResponses) {
+	// save the validators to the db
+	s.db.SetSync(abciResponsesKey, abciResponses.Bytes())
+}
+
+func (s *State) LoadABCIResponses() *ABCIResponses {
+	abciResponses := new(ABCIResponses)
+
+	buf := s.db.Get(abciResponsesKey)
+	if len(buf) != 0 {
+		r, n, err := bytes.NewReader(buf), new(int), new(error)
+		wire.ReadBinaryPtr(abciResponses, r, 0, n, err)
+		if *err != nil {
+			// DATA HAS BEEN CORRUPTED OR THE SPEC HAS CHANGED
+			Exit(Fmt("LoadABCIResponses: Data has been corrupted or its spec has changed: %v\n", *err))
+		}
+		// TODO: ensure that buf is completely read.
+	}
+	return abciResponses
+}
+
 func (s *State) Equals(s2 *State) bool {
 	return bytes.Equal(s.Bytes(), s2.Bytes())
 }
@@ -101,7 +130,22 @@ func (s *State) Bytes() []byte {
 
 // Mutate state variables to match block and validators
 // after running EndBlock
-func (s *State) SetBlockAndValidators(header *types.Header, blockPartsHeader types.PartSetHeader, prevValSet, nextValSet *types.ValidatorSet) {
+func (s *State) SetBlockAndValidators(header *types.Header, blockPartsHeader types.PartSetHeader, abciResponses *ABCIResponses) {
+
+	// copy the valset so we can apply changes from EndBlock
+	// and update s.LastValidators and s.Validators
+	prevValSet := s.Validators.Copy()
+	nextValSet := prevValSet.Copy()
+
+	// update the validator set with the latest abciResponses
+	err := updateValidators(nextValSet, abciResponses.EndBlock.Diffs)
+	if err != nil {
+		log.Warn("Error changing validator set", "error", err)
+		// TODO: err or carry on?
+	}
+	// Update validator accums and set state variables
+	nextValSet.IncrementAccum(1)
+
 	s.setBlockAndValidators(header.Height,
 		types.BlockID{header.Hash(), blockPartsHeader}, header.Time,
 		prevValSet, nextValSet)
@@ -134,6 +178,36 @@ func GetState(config cfg.Config, stateDB dbm.DB) *State {
 	return state
 }
 
+//--------------------------------------------------
+// ABCIResponses holds intermediate state during block processing
+
+type ABCIResponses struct {
+	Height int
+
+	DeliverTx []*abci.ResponseDeliverTx
+	EndBlock  abci.ResponseEndBlock
+
+	txs types.Txs // reference for indexing results by hash
+}
+
+func NewABCIResponses(block *types.Block) *ABCIResponses {
+	return &ABCIResponses{
+		Height:    block.Height,
+		DeliverTx: make([]*abci.ResponseDeliverTx, block.NumTxs),
+		txs:       block.Data.Txs,
+	}
+}
+
+// Serialize the ABCIResponse
+func (a *ABCIResponses) Bytes() []byte {
+	buf, n, err := new(bytes.Buffer), new(int), new(error)
+	wire.WriteBinary(*a, buf, n, err)
+	if *err != nil {
+		PanicCrisis(*err)
+	}
+	return buf.Bytes()
+}
+
 //-----------------------------------------------------------------------------
 // Genesis
 
diff --git a/state/state_test.go b/state/state_test.go
index a534cb695..dca83e801 100644
--- a/state/state_test.go
+++ b/state/state_test.go
@@ -1,8 +1,12 @@
 package state
 
 import (
+	"fmt"
 	"testing"
 
+	"github.com/stretchr/testify/assert"
+	abci "github.com/tendermint/abci/types"
+	"github.com/tendermint/go-crypto"
 	dbm "github.com/tendermint/go-db"
 	"github.com/tendermint/tendermint/config/tendermint_test"
 )
@@ -40,3 +44,30 @@ func TestStateSaveLoad(t *testing.T) {
 		t.Fatal("expected state and its copy to be identical. got %v\n expected %v\n", loadedState, state)
 	}
 }
+
+func TestABCIResponsesSaveLoad(t *testing.T) {
+	assert := assert.New(t)
+
+	config := tendermint_test.ResetConfig("state_")
+	stateDB := dbm.NewDB("state", config.GetString("db_backend"), config.GetString("db_dir"))
+	state := GetState(config, stateDB)
+
+	state.LastBlockHeight += 1
+
+	// build mock responses
+	block := makeBlock(2, state)
+	abciResponses := NewABCIResponses(block)
+	abciResponses.DeliverTx[0] = &abci.ResponseDeliverTx{Data: []byte("foo")}
+	abciResponses.DeliverTx[1] = &abci.ResponseDeliverTx{Data: []byte("bar"), Log: "ok"}
+	abciResponses.EndBlock = abci.ResponseEndBlock{Diffs: []*abci.Validator{
+		{
+			PubKey: crypto.GenPrivKeyEd25519().PubKey().Bytes(),
+			Power:  10,
+		},
+	}}
+	abciResponses.txs = nil
+
+	state.SaveABCIResponses(abciResponses)
+	abciResponses2 := state.LoadABCIResponses()
+	assert.Equal(abciResponses, abciResponses2, fmt.Sprintf("ABCIResponses don't match: Got %v, Expected %v", abciResponses2, abciResponses))
+}