diff --git a/src/pkg/archive/tar/writer_test.go b/src/pkg/archive/tar/writer_test.go
index 48b8911..838cb7e 100644
--- a/src/pkg/archive/tar/writer_test.go
+++ b/src/pkg/archive/tar/writer_test.go
@@ -150,5 +150,8 @@
 			t.Errorf("test %d: Incorrect result: (-=expected, +=actual)\n%v",
 				i, bytediff(expected, actual))
 		}
+		if testing.Short() { // The second test is expensive.
+			break
+		}
 	}
 }
diff --git a/src/pkg/big/int_test.go b/src/pkg/big/int_test.go
index c0cc9ac..9c19dd5 100755
--- a/src/pkg/big/int_test.go
+++ b/src/pkg/big/int_test.go
@@ -716,18 +716,25 @@
 
 
 func TestProbablyPrime(t *testing.T) {
+	nreps := 20
+	if testing.Short() {
+		nreps = 1
+	}
 	for i, s := range primes {
 		p, _ := new(Int).SetString(s, 10)
-		if !ProbablyPrime(p, 20) {
+		if !ProbablyPrime(p, nreps) {
 			t.Errorf("#%d prime found to be non-prime (%s)", i, s)
 		}
 	}
 
 	for i, s := range composites {
 		c, _ := new(Int).SetString(s, 10)
-		if ProbablyPrime(c, 20) {
+		if ProbablyPrime(c, nreps) {
 			t.Errorf("#%d composite found to be prime (%s)", i, s)
 		}
+		if testing.Short() {
+			break
+		}
 	}
 }
 
diff --git a/src/pkg/container/vector/numbers_test.go b/src/pkg/container/vector/numbers_test.go
index d540ace..b83b0bf 100644
--- a/src/pkg/container/vector/numbers_test.go
+++ b/src/pkg/container/vector/numbers_test.go
@@ -33,6 +33,9 @@
 
 
 func TestVectorNums(t *testing.T) {
+	if testing.Short() {
+		return
+	}
 	var v Vector
 	c := int(0)
 	runtime.GC()
@@ -51,6 +54,9 @@
 
 
 func TestIntVectorNums(t *testing.T) {
+	if testing.Short() {
+		return
+	}
 	var v IntVector
 	c := int(0)
 	runtime.GC()
@@ -69,6 +75,9 @@
 
 
 func TestStringVectorNums(t *testing.T) {
+	if testing.Short() {
+		return
+	}
 	var v StringVector
 	c := ""
 	runtime.GC()
diff --git a/src/pkg/crypto/elliptic/elliptic_test.go b/src/pkg/crypto/elliptic/elliptic_test.go
index 6ae6fb9..02083a9 100644
--- a/src/pkg/crypto/elliptic/elliptic_test.go
+++ b/src/pkg/crypto/elliptic/elliptic_test.go
@@ -297,6 +297,9 @@
 		if fmt.Sprintf("%x", x) != e.x || fmt.Sprintf("%x", y) != e.y {
 			t.Errorf("%d: bad output for k=%s: got (%x, %s), want (%s, %s)", i, e.k, x, y, e.x, e.y)
 		}
+		if testing.Short() && i > 5 {
+			break
+		}
 	}
 }
 
diff --git a/src/pkg/crypto/tls/handshake_messages_test.go b/src/pkg/crypto/tls/handshake_messages_test.go
index 21577dd..0b93b89 100644
--- a/src/pkg/crypto/tls/handshake_messages_test.go
+++ b/src/pkg/crypto/tls/handshake_messages_test.go
@@ -34,7 +34,11 @@
 	for i, iface := range tests {
 		ty := reflect.NewValue(iface).Type()
 
-		for j := 0; j < 100; j++ {
+		n := 100
+		if testing.Short() {
+			n = 5
+		}
+		for j := 0; j < n; j++ {
 			v, ok := quick.Value(ty, rand)
 			if !ok {
 				t.Errorf("#%d: failed to create value", i)
diff --git a/src/pkg/exp/eval/eval_test.go b/src/pkg/exp/eval/eval_test.go
index ff28cf1..541d3fe 100644
--- a/src/pkg/exp/eval/eval_test.go
+++ b/src/pkg/exp/eval/eval_test.go
@@ -39,9 +39,13 @@
 }
 
 func runTests(t *testing.T, baseName string, tests []test) {
-	for i, test := range tests {
+	delta := 1
+	if testing.Short() {
+		delta = 16
+	}
+	for i := 0; i < len(tests); i += delta {
 		name := fmt.Sprintf("%s[%d]", baseName, i)
-		test.run(t, name)
+		tests[i].run(t, name)
 	}
 }
 
diff --git a/src/pkg/fmt/fmt_test.go b/src/pkg/fmt/fmt_test.go
index c8aa609..4d308ac 100644
--- a/src/pkg/fmt/fmt_test.go
+++ b/src/pkg/fmt/fmt_test.go
@@ -442,6 +442,9 @@
 }
 
 func TestCountMallocs(t *testing.T) {
+	if testing.Short() {
+		return
+	}
 	mallocs := 0 - runtime.MemStats.Mallocs
 	for i := 0; i < 100; i++ {
 		Sprintf("")
diff --git a/src/pkg/go/printer/printer_test.go b/src/pkg/go/printer/printer_test.go
index debd2d3..72ce581 100644
--- a/src/pkg/go/printer/printer_test.go
+++ b/src/pkg/go/printer/printer_test.go
@@ -156,12 +156,15 @@
 
 
 func TestFiles(t *testing.T) {
-	for _, e := range data {
+	for i, e := range data {
 		source := filepath.Join(dataDir, e.source)
 		golden := filepath.Join(dataDir, e.golden)
 		check(t, source, golden, e.mode)
 		// TODO(gri) check that golden is idempotent
-		//check(t, golden, golden, e.mode);
+		//check(t, golden, golden, e.mode)
+		if testing.Short() && i >= 3 {
+			break
+		}
 	}
 }
 
diff --git a/src/pkg/image/png/reader_test.go b/src/pkg/image/png/reader_test.go
index 8314a83..0b2058d 100644
--- a/src/pkg/image/png/reader_test.go
+++ b/src/pkg/image/png/reader_test.go
@@ -34,6 +34,12 @@
 	"basn6a16",
 }
 
+var filenamesShort = []string{
+	"basn0g01",
+	"basn0g04-31",
+	"basn6a16",
+}
+
 func readPng(filename string) (image.Image, os.Error) {
 	f, err := os.Open(filename, os.O_RDONLY, 0444)
 	if err != nil {
@@ -157,7 +163,11 @@
 }
 
 func TestReader(t *testing.T) {
-	for _, fn := range filenames {
+	names := filenames
+	if testing.Short() {
+		names = filenamesShort
+	}
+	for _, fn := range names {
 		// Read the .png file.
 		img, err := readPng("testdata/pngsuite/" + fn + ".png")
 		if err != nil {
diff --git a/src/pkg/image/png/writer_test.go b/src/pkg/image/png/writer_test.go
index f218a55..4d9929f 100644
--- a/src/pkg/image/png/writer_test.go
+++ b/src/pkg/image/png/writer_test.go
@@ -32,7 +32,11 @@
 
 func TestWriter(t *testing.T) {
 	// The filenames variable is declared in reader_test.go.
-	for _, fn := range filenames {
+	names := filenames
+	if testing.Short() {
+		names = filenamesShort
+	}
+	for _, fn := range names {
 		qfn := "testdata/pngsuite/" + fn + ".png"
 		// Read the image.
 		m0, err := readPng(qfn)
diff --git a/src/pkg/json/decode_test.go b/src/pkg/json/decode_test.go
index ad60263..aad8b63 100644
--- a/src/pkg/json/decode_test.go
+++ b/src/pkg/json/decode_test.go
@@ -157,6 +157,7 @@
 }
 
 func TestUnmarshalMarshal(t *testing.T) {
+	initBig()
 	var v interface{}
 	if err := Unmarshal(jsonBig, &v); err != nil {
 		t.Fatalf("Unmarshal: %v", err)
diff --git a/src/pkg/json/scanner_test.go b/src/pkg/json/scanner_test.go
index 2dc8ff8..0d4de32 100644
--- a/src/pkg/json/scanner_test.go
+++ b/src/pkg/json/scanner_test.go
@@ -85,6 +85,7 @@
 // Tests of a large random structure.
 
 func TestCompactBig(t *testing.T) {
+	initBig()
 	var buf bytes.Buffer
 	if err := Compact(&buf, jsonBig); err != nil {
 		t.Fatalf("Compact: %v", err)
@@ -98,6 +99,7 @@
 }
 
 func TestIndentBig(t *testing.T) {
+	initBig()
 	var buf bytes.Buffer
 	if err := Indent(&buf, jsonBig, "", "\t"); err != nil {
 		t.Fatalf("Indent1: %v", err)
@@ -135,6 +137,7 @@
 }
 
 func TestNextValueBig(t *testing.T) {
+	initBig()
 	var scan scanner
 	item, rest, err := nextValue(jsonBig, &scan)
 	if err != nil {
@@ -160,6 +163,7 @@
 }
 
 func BenchmarkSkipValue(b *testing.B) {
+	initBig()
 	var scan scanner
 	for i := 0; i < b.N; i++ {
 		nextValue(jsonBig, &scan)
@@ -191,12 +195,23 @@
 
 var jsonBig []byte
 
-func init() {
-	b, err := Marshal(genValue(10000))
-	if err != nil {
-		panic(err)
+const (
+	big   = 10000
+	small = 100
+)
+
+func initBig() {
+	n := big
+	if testing.Short() {
+		n = small
 	}
-	jsonBig = b
+	if len(jsonBig) != n {
+		b, err := Marshal(genValue(n))
+		if err != nil {
+			panic(err)
+		}
+		jsonBig = b
+	}
 }
 
 func genValue(n int) interface{} {
diff --git a/src/pkg/netchan/netchan_test.go b/src/pkg/netchan/netchan_test.go
index 1b5c560..fd4d8f78 100644
--- a/src/pkg/netchan/netchan_test.go
+++ b/src/pkg/netchan/netchan_test.go
@@ -399,7 +399,7 @@
 
 func testFlow(sendDone chan bool, ch <-chan int, N int, t *testing.T) {
 	go func() {
-		time.Sleep(1e9)
+		time.Sleep(0.5e9)
 		sendDone <- false
 	}()
 
diff --git a/src/pkg/utf8/string_test.go b/src/pkg/utf8/string_test.go
index 9dd8472..f376b62 100644
--- a/src/pkg/utf8/string_test.go
+++ b/src/pkg/utf8/string_test.go
@@ -45,7 +45,12 @@
 	}
 }
 
-const randCount = 100000
+func randCount() int {
+	if testing.Short() {
+		return 100
+	}
+	return 100000
+}
 
 func TestRandomAccess(t *testing.T) {
 	for _, s := range testStrings {
@@ -58,7 +63,7 @@
 			t.Errorf("%s: expected %d runes; got %d", s, len(runes), str.RuneCount())
 			break
 		}
-		for j := 0; j < randCount; j++ {
+		for j := 0; j < randCount(); j++ {
 			i := rand.Intn(len(runes))
 			expect := runes[i]
 			got := str.At(i)
@@ -80,7 +85,7 @@
 			t.Errorf("%s: expected %d runes; got %d", s, len(runes), str.RuneCount())
 			break
 		}
-		for k := 0; k < randCount; k++ {
+		for k := 0; k < randCount(); k++ {
 			i := rand.Intn(len(runes))
 			j := rand.Intn(len(runes) + 1)
 			if i > j { // include empty strings