diff --git a/blocks/block.go b/blocks/block.go
index 70a247b5a..37b5ce439 100644
--- a/blocks/block.go
+++ b/blocks/block.go
@@ -7,12 +7,10 @@ import (
 )
 
 /* Block */
-
 type Block struct {
 	Header
 	Validation
 	Txs
-	// Checkpoint
 }
 
 func ReadBlock(r io.Reader) *Block {
@@ -35,7 +33,6 @@ func (self *Block) WriteTo(w io.Writer) (n int64, err error) {
 }
 
 /* Block > Header */
-
 type Header struct {
 	Name           String
 	Height         UInt64
@@ -70,7 +67,6 @@ func (self *Header) WriteTo(w io.Writer) (n int64, err error) {
 }
 
 /* Block > Validation */
-
 type Validation struct {
 	Signatures  []Signature
 	Adjustments []Adjustment
@@ -106,7 +102,6 @@ func (self *Validation) WriteTo(w io.Writer) (n int64, err error) {
 }
 
 /* Block > Txs */
-
 type Txs struct {
 	Txs []Tx
 }
diff --git a/blocks/block_manager.go b/blocks/block_manager.go
index 2654645fb..4dd44959b 100644
--- a/blocks/block_manager.go
+++ b/blocks/block_manager.go
@@ -13,22 +13,55 @@ const (
 	msgTypeRequest = Byte(0x02)
 	msgTypeData    = Byte(0x03)
 
-	DataTypeFullBlock  = byte(0x00)
-	DataTypeValidation = byte(0x01)
-	DataTypeTxs        = byte(0x02)
-	// dataTypeCheckpoint = byte(0x04)
-
 	dbKeyState = "state"
 )
 
-/*
- */
+//-----------------------------------------------------------------------------
+
+// We request each item separately.
+
+const (
+	dataTypeHeader     = byte(0x01)
+	dataTypeValidation = byte(0x02)
+	dataTypeTxs        = byte(0x03)
+)
+
+func _dataKey(dataType byte, height int) {
+	switch dataType {
+	case dataTypeHeader:
+		return fmt.Sprintf("H%v", height)
+	case dataTypeValidation:
+		return fmt.Sprintf("V%v", height)
+	case dataTypeTxs:
+		return fmt.Sprintf("T%v", height)
+	default:
+		panic("Unknown datatype %X", dataType)
+	}
+}
+
+func dataTypeFromObj(data interface{}) {
+	switch data.(type) {
+	case *Header:
+		return dataTypeHeader
+	case *Validation:
+		return dataTypeValidation
+	case *Txs:
+		return dataTypeTxs
+	default:
+		panic("Unexpected datatype: %v", data)
+	}
+}
+
+//-----------------------------------------------------------------------------
+
+// TODO: document
 type BlockManager struct {
 	db         *db_.LevelDB
 	sw         *p2p.Switch
 	swEvents   chan interface{}
 	state      blockManagerState
-	peerStates map[string]*blockManagerState
+	dataStates map[string]*dataState // TODO: replace with CMap
+	peerStates map[string]*peerState // TODO: replace with CMap
 	quit       chan struct{}
 	started    uint32
 	stopped    uint32
@@ -41,7 +74,8 @@ func NewBlockManager(sw *p2p.Switch, db *db_.LevelDB) *BlockManager {
 		db:         db,
 		sw:         sw,
 		swEvents:   swEvents,
-		peerStates: make(map[string]*blockManagerState),
+		dataStates: make(map[string]*dataState),
+		peerStates: make(map[string]*peerState),
 		quit:       make(chan struct{}),
 	}
 	bm.loadState()
@@ -63,13 +97,29 @@ func (bm *BlockManager) Stop() {
 	}
 }
 
-func (bm *BlockManager) StoreData(dataType byte, dataObj interface{}) {
-	// Validate data if possible.
+// NOTE: assumes that data is already validated.
+func (bm *BlockManager) StoreData(dataObj interface{}) {
+	bm.mtx.Lock()
+	defer bm.mtx.Unlock()
+	dataType := dataTypeForObj(dataObj)
+	dataKey := _dataKey(dataType, dataObj)
+	// Update state
+	// TODO
+	// Remove dataState entry, we'll no longer request this.
+	_dataState := bm.dataStates[dataKey]
+	removedRequests := _dataState.removeRequestsForDataType(dataType)
+	for _, request := range removedRequests {
+		// TODO in future, notify peer that the request has been canceled.
+		// No point doing this yet, requests in blocksCh are handled singlethreaded.
+	}
+	// What are we doing here?
+	_peerState := bm.peerstates[dataKey]
+
 	// If we have new data that extends our contiguous range, then announce it.
 }
 
-func (bm *BlockManager) LoadData(dataType byte) interface{} {
-	// NOTE: who's calling?
+func (bm *BlockManager) LoadData(dataType byte, height int) interface{} {
+	panic("not yet implemented")
 }
 
 func (bm *BlockManager) loadState() {
@@ -93,6 +143,7 @@ func (bm *BlockManager) saveState() {
 	bm.db.Set(dbKeyState, stateBytes)
 }
 
+// Handle peer new/done events
 func (bm *BlockManager) switchEventsHandler() {
 	for {
 		swEvent, ok := <-bm.swEvents
@@ -103,46 +154,169 @@ func (bm *BlockManager) switchEventsHandler() {
 		case p2p.SwitchEventNewPeer:
 			event := swEvent.(p2p.SwitchEventNewPeer)
 			// Create entry in .peerStates
+			bm.peerStates[event.Peer.RemoteAddress().String()] = &peerState{}
 			// Share our state with event.Peer
-			event.Peer
+			msg := &stateMessage{
+				lastHeaderHeight:     bm.state.lastHeaderHeight,
+				lastValidationHeight: bm.state.lastValidationHeight,
+				lastTxsHeight:        bm.state.lastTxsHeight,
+			}
+			tm := p2p.TypedMessage{msgTypeRequest, msg}
+			event.Peer.TrySend(NewPacket(blocksCh, tm))
 		case p2p.SwitchEventDonePeer:
 			// Remove entry from .peerStates
+			delete(bm.peerStates, event.Peer.RemoteAddress().String())
+		default:
+			log.Warning("Unhandled switch event type")
 		}
 	}
 }
 
+// Handle requests from the blocks channel
+func (bm *BlockManager) requestsHandler() {
+	for {
+		inPkt := bm.sw.Receive(blocksCh) // {Peer, Time, Packet}
+		if inPkt == nil {
+			// Client has stopped
+			break
+		}
+
+		// decode message
+		msg := decodeMessage(inPkt.Bytes)
+		log.Info("requestHandler received %v", msg)
+
+		switch msg.(type) {
+		case *stateMessage:
+			m := msg.(*stateMessage)
+			peerState := bm.peerStates[inPkt.Peer.RemoteAddress.String()]
+			if peerState == nil {
+				continue // peer has since been disconnected.
+			}
+			peerState.applyStateMessage(m)
+			// Consider requesting data.
+			// 1. if has more validation and we want it
+			// 2. if has more txs and we want it
+			// if peerState.estimatedCredit() >= averageBlock
+
+			// TODO: keep track of what we've requested from peer.
+			// TODO: keep track of from which peers we've requested data.
+			// TODO: be fair.
+		case *requestMessage:
+			// TODO: prevent abuse.
+		case *dataMessage:
+			// See if we want the data.
+			// Validate data.
+			// Add to db.
+			// Update state & broadcast as necessary.
+		default:
+			// Ignore unknown message
+			// bm.sw.StopPeerForError(inPkt.Peer, errInvalidMessage)
+		}
+	}
+
+	// Cleanup
+}
+
 //-----------------------------------------------------------------------------
 
-/* This is just to persist the block manager state in the db. */
+// blockManagerState keeps track of which block parts are stored locally.
+// It's also persisted via JSON in the db.
 type blockManagerState struct {
-	LastHeaderHeight       uint64 // Last contiguous header height
-	OtherHeaderHeights     []uint64
-	LastValidationHeight   uint64 // Last contiguous validation height
-	OtherValidationHeights []uint64
-	LastTxsHeight          uint64 // Last contiguous txs height
-	OtherTxsHeights        []uint64
+	lastHeaderHeight       uint64 // Last contiguous header height
+	lastValidationHeight   uint64 // Last contiguous validation height
+	lastTxsHeight          uint64 // Last contiguous txs height
+	otherHeaderHeights     []uint64
+	otherValidationHeights []uint64
+	otherTxsHeights        []uint64
 }
 
 //-----------------------------------------------------------------------------
 
-/*
-Each part of a block are stored separately in the db.
-*/
+// dataRequest keeps track of each request for a given peice of data & peer.
+type dataRequest struct {
+	peer     *p2p.Peer
+	dataType byte
+	height   uint64
+	time     time.Time
+}
+
+//-----------------------------------------------------------------------------
 
-func headerKey(height int) {
-	return fmt.Sprintf("B%v", height)
+// dataState keeps track of all requests for a given piece of data.
+type dataState struct {
+	mtx      sync.Mutex
+	requests []*dataRequest
 }
 
-func validationKey(height int) {
-	return fmt.Sprintf("V%v", height)
+func (ds *dataState) removeRequestsForDataType(dataType byte) []*dataRequest {
+	ds.mtx.Lock()
+	defer ds.mtx.Lock()
+	requests := []*dataRequest{}
+	filtered := []*dataRequest{}
+	for _, request := range ds.requests {
+		if request.dataType == dataType {
+			filtered = append(filtered, request)
+		} else {
+			requests = append(requests, request)
+		}
+	}
+	ds.requests = requests
+	return filtered
 }
 
-func txsKey(height int) {
-	return fmt.Sprintf("T%v", height)
+//-----------------------------------------------------------------------------
+
+// XXX
+type peerState struct {
+	mtx                  sync.Mutex
+	lastHeaderHeight     uint64 // Last contiguous header height
+	lastValidationHeight uint64 // Last contiguous validation height
+	lastTxsHeight        uint64 // Last contiguous txs height
+	dataBytesSent        uint64 // Data bytes sent to peer
+	dataBytesReceived    uint64 // Data bytes received from peer
+	numItemsReceived     uint64 // Number of data items received
+	numItemsUnreceived   uint64 // Number of data items requested but not received
+	numItemsSent         uint64 // Number of data items sent
+	requests             map[string]*dataRequest
 }
 
-func checkpointKey(height int) {
-	return fmt.Sprintf("C%v", height)
+func (ps *peerState) applyStateMessage(msg *stateMessage) {
+	ps.mtx.Lock()
+	defer ps.mtx.Unlock()
+	ps.lastHeaderHeight = msg.lastHeaderHeight
+	ps.lastValidationHeight = msg.lastValidationHeight
+	ps.lastTxsHeight = msg.lastTxsHeight
+}
+
+// Call this function for each data item received from peer, if the item was requested.
+// If the request timed out, dataBytesReceived is set to 0 to denote failure.
+func (ps *peerState) didReceiveData(dataKey string, dataBytesReceived uint64) {
+	ps.mtx.Lock()
+	defer ps.mtx.Lock()
+	request := ps.requests[dataKey]
+	if request == nil {
+		log.Warning("Could not find peerState request with dataKey %v", dataKey)
+		return
+	}
+	if dataBytesReceived == 0 {
+		ps.numItemsUnreceived += 1
+	} else {
+		ps.dataBytesReceived += dataBytesReceived
+		ps.numItemsReceived += 1
+	}
+	delete(ps.requests, dataKey)
+}
+
+// Call this function for each data item sent to peer, if the item was requested.
+func (ps *peerState) didSendData(dataKey string, dataBytesSent uint64) {
+	ps.mtx.Lock()
+	defer ps.mtx.Lock()
+	if dataBytesSent == 0 {
+		log.Warning("didSendData expects dataBytesSent > 0")
+		return
+	}
+	ps.dataBytesSent += dataBytesSent
+	ps.numItemsSent += 1
 }
 
 //-----------------------------------------------------------------------------
@@ -154,7 +328,7 @@ func decodeMessage(bz ByteSlice) (msg Message) {
 	// log.Debug("decoding msg bytes: %X", bz)
 	switch Byte(bz[0]) {
 	case msgTypeState:
-		return &StateMessage{}
+		return &stateMessage{}
 	case msgTypeRequest:
 		return readRequestMessage(bytes.NewReader(bz[1:]))
 	case msgTypeData:
@@ -165,93 +339,95 @@ func decodeMessage(bz ByteSlice) (msg Message) {
 }
 
 /*
-A StateMessage declares what (contiguous) blocks & headers are known.
-
-LastValidationHeight >= LastBlockHeight.
+A stateMessage declares what (contiguous) blocks & headers are known.
 */
-type StateMessage struct {
-	LastBlockHeight      UInt64
-	LastValidationHeight UInt64
+type stateMessage struct {
+	lastHeaderHeight     uint64 // Last contiguous header height
+	lastValidationHeight uint64 // Last contiguous validation height
+	lastTxsHeight        uint64 // Last contiguous txs height
 }
 
-func readStateMessage(r io.Reader) *StateMessage {
-	lastBlockHeight := ReadUInt64(r)
+func readStateMessage(r io.Reader) *stateMessage {
+	lastHeaderHeight := ReadUInt64(r)
 	lastValidationHeight := ReadUInt64(r)
-	return &StateMessage{
-		LastBlockHeight:      lastBlockHeight,
-		LastValidationHeight: lastValidationHeight,
+	lastTxsHeight := ReadUInt64(r)
+	return &stateMessage{
+		lastHeaderHeight:     lastHeaderHeight,
+		lastValidationHeight: lastValidationHeight,
+		lastTxsHeight:        lastTxsHeight,
 	}
 }
 
-func (m *StateMessage) WriteTo(w io.Writer) (n int64, err error) {
+func (m *stateMessage) WriteTo(w io.Writer) (n int64, err error) {
 	n, err = WriteTo(msgTypeState, w, n, err)
-	n, err = WriteTo(m.LastBlockHeight, w, n, err)
-	n, err = WriteTo(m.LastValidationHeight, w, n, err)
+	n, err = WriteTo(m.lastHeaderHeight, w, n, err)
+	n, err = WriteTo(m.lastValidationHeight, w, n, err)
+	n, err = WriteTo(m.lastTxsHeight, w, n, err)
 	return
 }
 
-func (m *StateMessage) String() string {
-	return fmt.Sprintf("[State %v/%v]",
-		m.LastBlockHeight, m.LastValidationHeight)
+func (m *stateMessage) String() string {
+	return fmt.Sprintf("[State %v/%v/%v]",
+		m.lastHeaderHeight, m.lastValidationHeight, m.lastTxsHeight)
 }
 
 /*
-A RequestMessage requests a block and/or header at a given height.
+A requestMessage requests a block and/or header at a given height.
 */
-type RequestMessage struct {
-	Type   Byte
-	Height UInt64
+type requestMessage struct {
+	dataType Byte
+	height   UInt64
 }
 
-func readRequestMessage(r io.Reader) *RequestMessage {
+func readRequestMessage(r io.Reader) *requestMessage {
 	requestType := ReadByte(r)
 	height := ReadUInt64(r)
-	return &RequestMessage{
-		Type:   requestType,
-		Height: height,
+	return &requestMessage{
+		dataType: requestType,
+		height:   height,
 	}
 }
 
-func (m *RequestMessage) WriteTo(w io.Writer) (n int64, err error) {
+func (m *requestMessage) WriteTo(w io.Writer) (n int64, err error) {
 	n, err = WriteTo(msgTypeRequest, w, n, err)
-	n, err = WriteTo(m.Type, w, n, err)
-	n, err = WriteTo(m.Height, w, n, err)
+	n, err = WriteTo(m.dataType, w, n, err)
+	n, err = WriteTo(m.height, w, n, err)
 	return
 }
 
-func (m *RequestMessage) String() string {
-	return fmt.Sprintf("[Request %X@%v]", m.Type, m.Height)
+func (m *requestMessage) String() string {
+	return fmt.Sprintf("[Request %X@%v]", m.dataType, m.height)
 }
 
 /*
-A DataMessage contains block data, maybe requested.
+A dataMessage contains block data, maybe requested.
 The data can be a Validation, Txs, or whole Block object.
 */
-type DataMessage struct {
-	Type   Byte
-	Height UInt64
-	Bytes  ByteSlice
+type dataMessage struct {
+	dataType Byte
+	height   UInt64
+	bytes    ByteSlice
 }
 
-func readDataMessage(r io.Reader) *DataMessage {
+func readDataMessage(r io.Reader) *dataMessage {
 	dataType := ReadByte(r)
 	height := ReadUInt64(r)
 	bytes := ReadByteSlice(r)
-	return &DataMessage{
-		Type:   dataType,
-		Height: height,
-		Bytes:  bytes,
+	return &dataMessage{
+		dataType: dataType,
+		height:   height,
+		bytes:    bytes,
 	}
 }
 
-func (m *DataMessage) WriteTo(w io.Writer) (n int64, err error) {
+func (m *dataMessage) WriteTo(w io.Writer) (n int64, err error) {
 	n, err = WriteTo(msgTypeData, w, n, err)
-	n, err = WriteTo(m.Type, w, n, err)
-	n, err = WriteTo(m.Height, w, n, err)
-	n, err = WriteTo(m.Bytes, w, n, err)
+	n, err = WriteTo(m.dataType, w, n, err)
+	n, err = WriteTo(m.height, w, n, err)
+	n, err = WriteTo(m.bytes, w, n, err)
 	return
 }
 
-func (m *DataMessage) String() string {
-	return fmt.Sprintf("[Data %X@%v]", m.Type, m.Height)
+func (m *dataMessage) String() string {
+	return fmt.Sprintf("[Data %X@%v]", m.dataType, m.height)
 }
diff --git a/p2p/peer.go b/p2p/peer.go
index 0ff2ecbdb..1fa2d0cac 100644
--- a/p2p/peer.go
+++ b/p2p/peer.go
@@ -59,10 +59,6 @@ func (p *Peer) IsOutbound() bool {
 	return p.outbound
 }
 
-func (p *Peer) LocalAddress() *NetAddress {
-	return p.conn.LocalAddress()
-}
-
 func (p *Peer) RemoteAddress() *NetAddress {
 	return p.conn.RemoteAddress()
 }
diff --git a/p2p/peer_manager.go b/p2p/peer_manager.go
index d331a230c..bbd8753bc 100644
--- a/p2p/peer_manager.go
+++ b/p2p/peer_manager.go
@@ -50,8 +50,8 @@ func (pm *PeerManager) Start() {
 	if atomic.CompareAndSwapUint32(&pm.started, 0, 1) {
 		log.Info("Starting PeerManager")
 		go pm.switchEventsHandler()
+		go pm.requestHandler()
 		go pm.ensurePeersHandler()
-		go pm.pexHandler()
 	}
 }
 
@@ -167,7 +167,7 @@ func (pm *PeerManager) ensurePeers() {
 }
 
 // Handles incoming PEX messages.
-func (pm *PeerManager) pexHandler() {
+func (pm *PeerManager) requestHandler() {
 
 	for {
 		inPkt := pm.sw.Receive(pexCh) // {Peer, Time, Packet}
@@ -178,7 +178,7 @@ func (pm *PeerManager) pexHandler() {
 
 		// decode message
 		msg := decodeMessage(inPkt.Bytes)
-		log.Info("pexHandler received %v", msg)
+		log.Info("requestHandler received %v", msg)
 
 		switch msg.(type) {
 		case *pexRequestMessage:
@@ -200,8 +200,8 @@ func (pm *PeerManager) pexHandler() {
 				pm.book.AddAddress(addr, srcAddr)
 			}
 		default:
-			// Bad peer.
-			pm.sw.StopPeerForError(inPkt.Peer, pexErrInvalidMessage)
+			// Ignore unknown message.
+			// pm.sw.StopPeerForError(inPkt.Peer, pexErrInvalidMessage)
 		}
 	}
 
diff --git a/p2p/switch.go b/p2p/switch.go
index 01ab970c8..03acb326e 100644
--- a/p2p/switch.go
+++ b/p2p/switch.go
@@ -43,6 +43,7 @@ func NewSwitch(channels []ChannelDescriptor) *Switch {
 	// make pktRecvQueues...
 	pktRecvQueues := make(map[string]chan *InboundPacket)
 	for _, chDesc := range channels {
+		// XXX: buffer this
 		pktRecvQueues[chDesc.Name] = make(chan *InboundPacket)
 	}