diff --git a/balancer.go b/balancer.go
index e1730166..5aeb646d 100644
--- a/balancer.go
+++ b/balancer.go
@@ -19,7 +19,6 @@
 package grpc
 
 import (
-	"fmt"
 	"net"
 	"sync"
 
@@ -118,26 +117,6 @@ type Balancer interface {
 	Close() error
 }
 
-// downErr implements net.Error. It is constructed by gRPC internals and passed to the down
-// call of Balancer.
-type downErr struct {
-	timeout   bool
-	temporary bool
-	desc      string
-}
-
-func (e downErr) Error() string   { return e.desc }
-func (e downErr) Timeout() bool   { return e.timeout }
-func (e downErr) Temporary() bool { return e.temporary }
-
-func downErrorf(timeout, temporary bool, format string, a ...interface{}) downErr {
-	return downErr{
-		timeout:   timeout,
-		temporary: temporary,
-		desc:      fmt.Sprintf(format, a...),
-	}
-}
-
 // RoundRobin returns a Balancer that selects addresses round-robin. It uses r to watch
 // the name resolution updates and updates the addresses available correspondingly.
 //
@@ -410,7 +389,3 @@ func (rr *roundRobin) Close() error {
 type pickFirst struct {
 	*roundRobin
 }
-
-func pickFirstBalancerV1(r naming.Resolver) Balancer {
-	return &pickFirst{&roundRobin{r: r}}
-}
diff --git a/balancer_test.go b/balancer_test.go
index 8675e7d5..d9b2eebe 100644
--- a/balancer_test.go
+++ b/balancer_test.go
@@ -39,6 +39,10 @@ import (
 	_ "google.golang.org/grpc/resolver/passthrough"
 )
 
+func pickFirstBalancerV1(r naming.Resolver) Balancer {
+	return &pickFirst{&roundRobin{r: r}}
+}
+
 type testWatcher struct {
 	// the channel to receives name resolution updates
 	update chan *naming.Update
diff --git a/channelz/service/service.go b/channelz/service/service.go
index 1cc607e6..4ffe1344 100644
--- a/channelz/service/service.go
+++ b/channelz/service/service.go
@@ -47,7 +47,7 @@ func convertToPtypesDuration(sec int64, usec int64) *durpb.Duration {
 
 // RegisterChannelzServiceToServer registers the channelz service to the given server.
 func RegisterChannelzServiceToServer(s *grpc.Server) {
-	channelzgrpc.RegisterChannelzServer(s, &serverImpl{})
+	channelzgrpc.RegisterChannelzServer(s, newCZServer())
 }
 
 func newCZServer() channelzgrpc.ChannelzServer {
diff --git a/clientconn.go b/clientconn.go
index bb6aeb8c..318ac407 100644
--- a/clientconn.go
+++ b/clientconn.go
@@ -65,8 +65,6 @@ var (
 	errConnDrain = errors.New("grpc: the connection is drained")
 	// errConnClosing indicates that the connection is closing.
 	errConnClosing = errors.New("grpc: the connection is closing")
-	// errConnUnavailable indicates that the connection is unavailable.
-	errConnUnavailable = errors.New("grpc: the connection is unavailable")
 	// errBalancerClosed indicates that the balancer is closed.
 	errBalancerClosed = errors.New("grpc: balancer is closed")
 	// We use an accessor so that minConnectTimeout can be
@@ -89,8 +87,6 @@ var (
 	// errCredentialsConflict indicates that grpc.WithTransportCredentials()
 	// and grpc.WithInsecure() are both called for a connection.
 	errCredentialsConflict = errors.New("grpc: transport credentials are set for an insecure connection (grpc.WithTransportCredentials() and grpc.WithInsecure() are both called)")
-	// errNetworkIO indicates that the connection is down due to some network I/O error.
-	errNetworkIO = errors.New("grpc: failed with network I/O error")
 )
 
 const (
@@ -856,14 +852,6 @@ func (ac *addrConn) printf(format string, a ...interface{}) {
 	}
 }
 
-// errorf records an error in ac's event log, unless ac has been closed.
-// REQUIRES ac.mu is held.
-func (ac *addrConn) errorf(format string, a ...interface{}) {
-	if ac.events != nil {
-		ac.events.Errorf(format, a...)
-	}
-}
-
 // resetTransport recreates a transport to the address for ac.  The old
 // transport will close itself on error or when the clientconn is closed.
 // The created transport must receive initial settings frame from the server.
diff --git a/credentials/alts/utils.go b/credentials/alts/utils.go
index 4cd1f8c9..49bdcdf7 100644
--- a/credentials/alts/utils.go
+++ b/credentials/alts/utils.go
@@ -29,7 +29,6 @@ import (
 	"regexp"
 	"runtime"
 	"strings"
-	"time"
 
 	"golang.org/x/net/context"
 	"google.golang.org/grpc/peer"
@@ -41,7 +40,6 @@ const (
 	windowsCheckCommandArgs  = "Get-WmiObject -Class Win32_BIOS"
 	powershellOutputFilter   = "Manufacturer"
 	windowsManufacturerRegex = ":(.*)"
-	windowsCheckTimeout      = 30 * time.Second
 )
 
 type platformError string
diff --git a/internal/transport/controlbuf.go b/internal/transport/controlbuf.go
index ce135c4d..204ba158 100644
--- a/internal/transport/controlbuf.go
+++ b/internal/transport/controlbuf.go
@@ -104,7 +104,6 @@ type headerFrame struct {
 
 type cleanupStream struct {
 	streamID uint32
-	idPtr    *uint32
 	rst      bool
 	rstCode  http2.ErrCode
 	onWrite  func()
@@ -138,9 +137,6 @@ type outgoingSettings struct {
 	ss []http2.Setting
 }
 
-type settingsAck struct {
-}
-
 type incomingGoAway struct {
 }
 
diff --git a/internal/transport/handler_server_test.go b/internal/transport/handler_server_test.go
index da04e7ce..d4e2ce3b 100644
--- a/internal/transport/handler_server_test.go
+++ b/internal/transport/handler_server_test.go
@@ -252,7 +252,6 @@ func newTestHandlerResponseWriter() http.ResponseWriter {
 type handleStreamTest struct {
 	t     *testing.T
 	bodyw *io.PipeWriter
-	req   *http.Request
 	rw    testHandlerResponseWriter
 	ht    *serverHandlerTransport
 }
diff --git a/internal/transport/log.go b/internal/transport/log.go
index ac8e358c..879df80c 100644
--- a/internal/transport/log.go
+++ b/internal/transport/log.go
@@ -42,9 +42,3 @@ func errorf(format string, args ...interface{}) {
 		grpclog.Errorf(format, args...)
 	}
 }
-
-func fatalf(format string, args ...interface{}) {
-	if grpclog.V(logLevel) {
-		grpclog.Fatalf(format, args...)
-	}
-}
diff --git a/internal/transport/transport.go b/internal/transport/transport.go
index 644cf11c..fdf8ad68 100644
--- a/internal/transport/transport.go
+++ b/internal/transport/transport.go
@@ -176,7 +176,6 @@ type Stream struct {
 	buf          *recvBuffer
 	trReader     io.Reader
 	fc           *inFlow
-	recvQuota    uint32
 	wq           *writeQuota
 
 	// Callback to state application's intentions to read data. This
diff --git a/internal/transport/transport_test.go b/internal/transport/transport_test.go
index 52be96f0..109b37bc 100644
--- a/internal/transport/transport_test.go
+++ b/internal/transport/transport_test.go
@@ -1747,13 +1747,6 @@ func TestContextErr(t *testing.T) {
 	}
 }
 
-func max(a, b int32) int32 {
-	if a > b {
-		return a
-	}
-	return b
-}
-
 type windowSizeConfig struct {
 	serverStream int32
 	serverConn   int32
diff --git a/interop/alts/client/client.go b/interop/alts/client/client.go
index 3710c4b3..b0776107 100644
--- a/interop/alts/client/client.go
+++ b/interop/alts/client/client.go
@@ -30,10 +30,6 @@ import (
 	testpb "google.golang.org/grpc/interop/grpc_testing"
 )
 
-const (
-	value = "test_value"
-)
-
 var (
 	hsAddr     = flag.String("alts_handshaker_service_address", "", "ALTS handshaker gRPC service address")
 	serverAddr = flag.String("server_address", ":8080", "The port on which the server is listening")
diff --git a/rpc_util.go b/rpc_util.go
index 207f0ee6..fa056830 100644
--- a/rpc_util.go
+++ b/rpc_util.go
@@ -156,13 +156,11 @@ type callInfo struct {
 	compressorType        string
 	failFast              bool
 	stream                *clientStream
-	traceInfo             traceInfo // in trace.go
 	maxReceiveMessageSize *int
 	maxSendMessageSize    *int
 	creds                 credentials.PerRPCCredentials
 	contentSubtype        string
 	codec                 baseCodec
-	disableRetry          bool
 	maxRetryRPCBufferSize int
 }
 
diff --git a/stats/stats_test.go b/stats/stats_test.go
index 00a5e4f3..c48143a3 100644
--- a/stats/stats_test.go
+++ b/stats/stats_test.go
@@ -403,7 +403,7 @@ const (
 	inTrailer
 	outPayload
 	outHeader
-	outTrailer
+	// TODO: test outTrailer ?
 	connbegin
 	connend
 )
diff --git a/test/end2end_test.go b/test/end2end_test.go
index 818532c2..c80804e8 100644
--- a/test/end2end_test.go
+++ b/test/end2end_test.go
@@ -3059,10 +3059,6 @@ func testSetAndSendHeaderStreamingRPC(t *testing.T, e env) {
 	defer te.tearDown()
 	tc := testpb.NewTestServiceClient(te.clientConn())
 
-	const (
-		argSize  = 1
-		respSize = 1
-	)
 	ctx := metadata.NewOutgoingContext(context.Background(), testMetadata)
 	stream, err := tc.FullDuplexCall(ctx)
 	if err != nil {
@@ -4659,9 +4655,7 @@ func TestCredsHandshakeAuthority(t *testing.T) {
 	}
 }
 
-type clientFailCreds struct {
-	got string
-}
+type clientFailCreds struct{}
 
 func (c *clientFailCreds) ServerHandshake(rawConn net.Conn) (net.Conn, credentials.AuthInfo, error) {
 	return rawConn, nil, nil