diff --git a/consensus/state.go b/consensus/state.go
index f5a0b636d..201586643 100644
--- a/consensus/state.go
+++ b/consensus/state.go
@@ -819,11 +819,7 @@ func (cs *ConsensusState) createProposalBlock() (block *types.Block, blockParts
 	}
 
 	// Mempool validated transactions
-	txs, err := cs.mempool.Reap()
-	if err != nil {
-		log.Warn("createProposalBlock: Error getting proposal txs", "error", err)
-		return nil, nil
-	}
+	txs := cs.mempool.Reap()
 
 	block = &types.Block{
 		Header: &types.Header{
diff --git a/mempool/mempool.go b/mempool/mempool.go
index 95b91d327..2af9bc0e1 100644
--- a/mempool/mempool.go
+++ b/mempool/mempool.go
@@ -1,9 +1,11 @@
 package mempool
 
 import (
+	"bytes"
 	"container/list"
 	"sync"
 	"sync/atomic"
+	"time"
 
 	"github.com/tendermint/go-clist"
 	. "github.com/tendermint/go-common"
@@ -36,16 +38,21 @@ Garbage collection of old elements from mempool.txs is handlde via
 the DetachPrev() call, which makes old elements not reachable by
 peer broadcastTxRoutine() automatically garbage collected.
 
+TODO: Better handle tmsp client errors. (make it automatically handle connection errors)
+
 */
 
 const cacheSize = 100000
 
 type Mempool struct {
-	proxyMtx     sync.Mutex
-	proxyAppConn proxy.AppConn
-	txs          *clist.CList // concurrent linked-list of good txs
-	counter      int64        // simple incrementing counter
-	height       int          // the last block Update()'d to
+	proxyMtx      sync.Mutex
+	proxyAppConn  proxy.AppConn
+	txs           *clist.CList    // concurrent linked-list of good txs
+	counter       int64           // simple incrementing counter
+	height        int             // the last block Update()'d to
+	rechecking    int32           // for re-checking filtered txs on Update()
+	recheckCursor *clist.CElement // next expected response
+	recheckEnd    *clist.CElement // re-checking stops here
 
 	// Keep a cache of already-seen txs.
 	// This reduces the pressure on the proxyApp.
@@ -55,10 +62,13 @@ type Mempool struct {
 
 func NewMempool(proxyAppConn proxy.AppConn) *Mempool {
 	mempool := &Mempool{
-		proxyAppConn: proxyAppConn,
-		txs:          clist.New(),
-		counter:      0,
-		height:       0,
+		proxyAppConn:  proxyAppConn,
+		txs:           clist.New(),
+		counter:       0,
+		height:        0,
+		rechecking:    0,
+		recheckCursor: nil,
+		recheckEnd:    nil,
 
 		cacheMap:  make(map[string]struct{}, cacheSize),
 		cacheList: list.New(),
@@ -102,6 +112,7 @@ func (mem *Mempool) CheckTx(tx types.Tx, cb func(*tmsp.Response)) (err error) {
 	mem.cacheList.PushBack(tx)
 	// END CACHE
 
+	// NOTE: proxyAppConn may error if tx buffer is full
 	if err = mem.proxyAppConn.Error(); err != nil {
 		return err
 	}
@@ -115,6 +126,14 @@ func (mem *Mempool) CheckTx(tx types.Tx, cb func(*tmsp.Response)) (err error) {
 
 // TMSP callback function
 func (mem *Mempool) resCb(req *tmsp.Request, res *tmsp.Response) {
+	if mem.recheckCursor == nil {
+		mem.resCbNormal(req, res)
+	} else {
+		mem.resCbRecheck(req, res)
+	}
+}
+
+func (mem *Mempool) resCbNormal(req *tmsp.Request, res *tmsp.Response) {
 	switch res.Type {
 	case tmsp.MessageType_CheckTx:
 		if res.Code == tmsp.CodeType_OK {
@@ -134,14 +153,47 @@ func (mem *Mempool) resCb(req *tmsp.Request, res *tmsp.Response) {
 	}
 }
 
+func (mem *Mempool) resCbRecheck(req *tmsp.Request, res *tmsp.Response) {
+	switch res.Type {
+	case tmsp.MessageType_CheckTx:
+		memTx := mem.recheckCursor.Value.(*mempoolTx)
+		if !bytes.Equal(req.Data, memTx.tx) {
+			PanicSanity(Fmt("Unexpected tx response from proxy during recheck\n"+
+				"Expected %X, got %X", req.Data, memTx.tx))
+		}
+		if res.Code == tmsp.CodeType_OK {
+			// Good, nothing to do.
+		} else {
+			// Tx became invalidated due to newly committed block.
+			mem.txs.Remove(mem.recheckCursor)
+			mem.recheckCursor.DetachPrev()
+		}
+		if mem.recheckCursor == mem.recheckEnd {
+			mem.recheckCursor = nil
+		} else {
+			mem.recheckCursor = mem.recheckCursor.Next()
+		}
+		if mem.recheckCursor == nil {
+			// Done!
+			atomic.StoreInt32(&mem.rechecking, 0)
+		}
+	default:
+		// ignore other messages
+	}
+}
+
 // Get the valid transactions remaining
-func (mem *Mempool) Reap() ([]types.Tx, error) {
+func (mem *Mempool) Reap() []types.Tx {
 	mem.proxyMtx.Lock()
 	defer mem.proxyMtx.Unlock()
 
-	txs := mem.collectTxs()
+	for atomic.LoadInt32(&mem.rechecking) > 0 {
+		// TODO: Something better?
+		time.Sleep(time.Millisecond * 10)
+	}
 
-	return txs, nil
+	txs := mem.collectTxs()
+	return txs
 }
 
 func (mem *Mempool) collectTxs() []types.Tx {
@@ -156,7 +208,7 @@ func (mem *Mempool) collectTxs() []types.Tx {
 // Tell mempool that these txs were committed.
 // Mempool will discard these txs.
 // NOTE: this should be called *after* block is committed by consensus.
-func (mem *Mempool) Update(height int, txs []types.Tx) error {
+func (mem *Mempool) Update(height int, txs []types.Tx) {
 	mem.proxyMtx.Lock()
 	defer mem.proxyMtx.Unlock()
 
@@ -168,11 +220,15 @@ func (mem *Mempool) Update(height int, txs []types.Tx) error {
 
 	// Set height
 	mem.height = height
-
 	// Remove transactions that are already in txs.
-	mem.filterTxs(txsMap)
-
-	return nil
+	goodTxs := mem.filterTxs(txsMap)
+	// Recheck mempool txs
+	// TODO: make optional
+	mem.recheckTxs(goodTxs)
+
+	// At this point, mem.txs are being rechecked.
+	// mem.recheckCursor re-scans mem.txs and possibly removes some txs.
+	// Before mem.Reap(), we should wait for mem.recheckCursor to be nil.
 }
 
 func (mem *Mempool) filterTxs(blockTxsMap map[string]struct{}) []types.Tx {
@@ -191,6 +247,23 @@ func (mem *Mempool) filterTxs(blockTxsMap map[string]struct{}) []types.Tx {
 	return goodTxs
 }
 
+// NOTE: pass in goodTxs because mem.txs can mutate concurrently.
+func (mem *Mempool) recheckTxs(goodTxs []types.Tx) {
+	if len(goodTxs) == 0 {
+		return
+	}
+	atomic.StoreInt32(&mem.rechecking, 1)
+	mem.recheckCursor = mem.txs.Front()
+	mem.recheckEnd = mem.txs.Back()
+
+	// Push txs to proxyAppConn
+	// NOTE: resCb() may be called concurrently.
+	for _, tx := range goodTxs {
+		mem.proxyAppConn.CheckTxAsync(tx)
+	}
+	mem.proxyAppConn.FlushAsync()
+}
+
 //--------------------------------------------------------------------------------
 
 // A transaction that successfully ran
diff --git a/mempool/mempool_test.go b/mempool/mempool_test.go
index b4a104239..1d93efc90 100644
--- a/mempool/mempool_test.go
+++ b/mempool/mempool_test.go
@@ -44,10 +44,7 @@ func TestSerialReap(t *testing.T) {
 	}
 
 	reapCheck := func(exp int) {
-		txs, err := mempool.Reap()
-		if err != nil {
-			t.Error("Error in mempool.Reap()", err)
-		}
+		txs := mempool.Reap()
 		if len(txs) != exp {
 			t.Fatalf("Expected to reap %v txs but got %v", exp, len(txs))
 		}
@@ -60,10 +57,7 @@ func TestSerialReap(t *testing.T) {
 			binary.BigEndian.PutUint64(txBytes, uint64(i))
 			txs = append(txs, txBytes)
 		}
-		err := mempool.Update(0, txs)
-		if err != nil {
-			t.Error("Error in mempool.Update()", err)
-		}
+		mempool.Update(0, txs)
 	}
 
 	commitRange := func(start, end int) {
diff --git a/rpc/core/mempool.go b/rpc/core/mempool.go
index 7befedbf8..61bf08a56 100644
--- a/rpc/core/mempool.go
+++ b/rpc/core/mempool.go
@@ -36,6 +36,6 @@ func BroadcastTxSync(tx types.Tx) (*ctypes.ResultBroadcastTx, error) {
 }
 
 func UnconfirmedTxs() (*ctypes.ResultUnconfirmedTxs, error) {
-	txs, err := mempoolReactor.Mempool.Reap()
-	return &ctypes.ResultUnconfirmedTxs{len(txs), txs}, err
+	txs := mempoolReactor.Mempool.Reap()
+	return &ctypes.ResultUnconfirmedTxs{len(txs), txs}, nil
 }