diff --git a/runtime/tests/vm/vm.status b/runtime/tests/vm/vm.status
index 3573d455af8..12b565ada88 100644
--- a/runtime/tests/vm/vm.status
+++ b/runtime/tests/vm/vm.status
@@ -6,3 +6,6 @@ prefix vm
 
 # When a spawned isolate throws an uncaught exception, we terminate the vm.
 RunLoop_Exception: Fail
+
+# Partially implemented old generation GC.
+OldGC: CRASH
diff --git a/runtime/vm/gc_marker.cc b/runtime/vm/gc_marker.cc
new file mode 100644
index 00000000000..48012921a9a
--- /dev/null
+++ b/runtime/vm/gc_marker.cc
@@ -0,0 +1,207 @@
+// Copyright (c) 2011, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+#include "vm/gc_marker.h"
+
+#include "vm/allocation.h"
+#include "vm/isolate.h"
+#include "vm/pages.h"
+#include "vm/raw_object.h"
+#include "vm/stack_frame.h"
+#include "vm/visitor.h"
+
+namespace dart {
+
+// A simple chunked marking stack.
+class MarkingStack : public ValueObject {
+ public:
+  MarkingStack()
+      : head_(new MarkingStackChunk()),
+        empty_chunks_(NULL),
+        marking_stack_(NULL),
+        top_(0) {
+    marking_stack_ = head_->MarkingStackChunkMemory();
+  }
+
+  ~MarkingStack() {
+    // TODO(iposva): Consider caching a couple emtpy marking stack chunks.
+    ASSERT(IsEmpty());
+    delete head_;
+    MarkingStackChunk* next;
+    while (empty_chunks_ != NULL) {
+      next = empty_chunks_->next();
+      delete empty_chunks_;
+      empty_chunks_ = next;
+    }
+  }
+
+  bool IsEmpty() const {
+    return IsMarkingStackChunkEmpty() && (head_->next() == NULL);
+  }
+
+  void Push(RawObject* value) {
+    ASSERT(!IsMarkingStackChunkFull());
+    marking_stack_[top_] = value;
+    top_++;
+    if (IsMarkingStackChunkFull()) {
+      MarkingStackChunk* new_chunk;
+      if (empty_chunks_ == NULL) {
+        new_chunk = new MarkingStackChunk();
+      } else {
+        new_chunk = empty_chunks_;
+        empty_chunks_ = new_chunk->next();
+      }
+      new_chunk->set_next(head_);
+      head_ = new_chunk;
+      marking_stack_ = head_->MarkingStackChunkMemory();
+      top_ = 0;
+    }
+  }
+
+  RawObject* Pop() {
+    ASSERT(head_ != NULL);
+    ASSERT(!IsEmpty());
+    if (IsMarkingStackChunkEmpty()) {
+      MarkingStackChunk* empty_chunk = head_;
+      head_ = head_->next();
+      empty_chunk->set_next(empty_chunks_);
+      empty_chunks_ = empty_chunk;
+      marking_stack_ = head_->MarkingStackChunkMemory();
+      top_ = MarkingStackChunk::kMarkingStackChunkSize;
+    }
+    top_--;
+    return marking_stack_[top_];
+  }
+
+ private:
+  class MarkingStackChunk {
+   public:
+    MarkingStackChunk() : next_(NULL) {}
+    ~MarkingStackChunk() {}
+
+    RawObject** MarkingStackChunkMemory() {
+      return &memory_[0];
+    }
+
+    MarkingStackChunk* next() const { return next_; }
+    void set_next(MarkingStackChunk* value) { next_ = value; }
+
+    static const uint32_t kMarkingStackChunkSize = 1024;
+
+   private:
+    RawObject* memory_[kMarkingStackChunkSize];
+    MarkingStackChunk* next_;
+
+    DISALLOW_COPY_AND_ASSIGN(MarkingStackChunk);
+  };
+
+  bool IsMarkingStackChunkFull() const {
+    return top_ == MarkingStackChunk::kMarkingStackChunkSize;
+  }
+
+  bool IsMarkingStackChunkEmpty() const {
+    return top_ == 0;
+  }
+
+  MarkingStackChunk* head_;
+  MarkingStackChunk* empty_chunks_;
+  RawObject** marking_stack_;
+  uint32_t top_;
+
+  DISALLOW_COPY_AND_ASSIGN(MarkingStack);
+};
+
+
+class MarkingVisitor : public ObjectPointerVisitor {
+ public:
+  MarkingVisitor(Heap* heap, PageSpace* page_space, MarkingStack* marking_stack)
+      : heap_(heap),
+        vm_heap_(Dart::vm_isolate()->heap()),
+        page_space_(page_space),
+        marking_stack_(marking_stack) {}
+
+  MarkingStack* marking_stack() const { return marking_stack_; }
+
+  void VisitPointers(RawObject** first, RawObject** last) {
+    for (RawObject** current = first; current <= last; current++) {
+      MarkObject(*current);
+    }
+  }
+
+ private:
+  void MarkAndPush(RawObject* raw_obj) {
+    ASSERT(raw_obj->IsHeapObject());
+
+    // Mark the object and push it on the marking stack.
+    ASSERT(!raw_obj->IsMarked());
+    RawClass* raw_class = raw_obj->ptr()->class_;
+    raw_obj->SetMarkBit();
+    marking_stack_->Push(raw_obj);
+
+    // TODO(iposva): Should we mark the classes early?
+    MarkObject(raw_class);
+  }
+
+  void MarkObject(RawObject* raw_obj) {
+    // Fast exit if the raw object is a Smi.
+    if (!raw_obj->IsHeapObject()) return;
+
+    // Fast exit if the raw object is marked.
+    if (raw_obj->IsMarked()) return;
+
+    // Skip over new objects, but verify consistency of heap while at it.
+    if (raw_obj->IsNewObject()) {
+      // TODO(iposva): Add consistency check.
+      return;
+    }
+
+    uword raw_addr = RawObject::ToAddr(raw_obj);
+    // TODO(iposva): Premark vm_isolate objects, to avoid this extra check here.
+    if (vm_heap_->Contains(raw_addr)) {
+      return;
+    }
+    // TODO(iposva): merge old and code spaces.
+    // ASSERT(page_space_->Contains(raw_addr));
+
+    MarkAndPush(raw_obj);
+  }
+
+  Heap* heap_;
+  Heap* vm_heap_;
+  PageSpace* page_space_;
+  MarkingStack* marking_stack_;
+
+  DISALLOW_IMPLICIT_CONSTRUCTORS(MarkingVisitor);
+};
+
+
+void GCMarker::Prologue(Isolate* isolate) {
+  // Nothing to do at the moment.
+}
+
+
+void GCMarker::IterateRoots(Isolate* isolate, MarkingVisitor* visitor) {
+  isolate->VisitObjectPointers(visitor,
+                               StackFrameIterator::kDontValidateFrames);
+  heap_->IterateNewPointers(visitor);
+}
+
+
+void GCMarker::DrainMarkingStack(Isolate* isolate, MarkingVisitor* visitor) {
+  while (!visitor->marking_stack()->IsEmpty()) {
+    RawObject* raw_obj = visitor->marking_stack()->Pop();
+    raw_obj->VisitPointers(visitor);
+  }
+}
+
+
+void GCMarker::MarkObjects(Isolate* isolate, PageSpace* page_space) {
+  MarkingStack marking_stack;
+  Prologue(isolate);
+  MarkingVisitor mark(heap_, page_space, &marking_stack);
+  IterateRoots(isolate, &mark);
+  DrainMarkingStack(isolate, &mark);
+}
+
+}  // namespace dart
diff --git a/runtime/vm/gc_marker.h b/runtime/vm/gc_marker.h
new file mode 100644
index 00000000000..4d46fd52eb7
--- /dev/null
+++ b/runtime/vm/gc_marker.h
@@ -0,0 +1,39 @@
+// Copyright (c) 2011, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+#ifndef VM_GC_MARKER_H_
+#define VM_GC_MARKER_H_
+
+#include "vm/allocation.h"
+
+namespace dart {
+
+// Forward declarations.
+class Heap;
+class Isolate;
+class MarkingVisitor;
+class PageSpace;
+
+// The class GCMarker is used to mark reachable old generation objects as part
+// of the mark-sweep collection. The marking bit used is defined in RawObject.
+class GCMarker : public ValueObject {
+ public:
+  explicit GCMarker(Heap* heap) : heap_(heap) { }
+  ~GCMarker() { }
+
+  void MarkObjects(Isolate* isolate, PageSpace* page_space);
+
+ private:
+  void Prologue(Isolate* isolate);
+  void IterateRoots(Isolate* isolate, MarkingVisitor* visitor);
+  void DrainMarkingStack(Isolate* isolate, MarkingVisitor* visitor);
+
+  Heap* heap_;
+
+  DISALLOW_IMPLICIT_CONSTRUCTORS(GCMarker);
+};
+
+}  // namespace dart
+
+#endif  // VM_GC_MARKER_H_
diff --git a/runtime/vm/heap.cc b/runtime/vm/heap.cc
index ba779b7cf12..2b39d1689e0 100644
--- a/runtime/vm/heap.cc
+++ b/runtime/vm/heap.cc
@@ -103,6 +103,53 @@ bool Heap::CodeContains(uword addr) const {
 }
 
 
+void Heap::IterateNewPointers(ObjectPointerVisitor* visitor) {
+  new_space_->VisitObjectPointers(visitor);
+}
+
+
+void Heap::IterateOldPointers(ObjectPointerVisitor* visitor) {
+  old_space_->VisitObjectPointers(visitor);
+  code_space_->VisitObjectPointers(visitor);
+}
+
+
+void Heap::CollectGarbage(Space space) {
+  switch (space) {
+    case kNew:
+      new_space_->Scavenge();
+      break;
+    case kOld:
+      old_space_->MarkSweep();
+      break;
+    case kExecutable:
+      UNIMPLEMENTED();
+      code_space_->MarkSweep();
+      break;
+    default:
+      UNREACHABLE();
+  }
+}
+
+
+void Heap::CollectAllGarbage() {
+  new_space_->Scavenge();
+  old_space_->MarkSweep();
+  // TODO(iposva): Merge old and code space.
+  // code_space_->MarkSweep();
+}
+
+
+uword Heap::TopAddress() {
+  return reinterpret_cast<uword>(new_space_->TopAddress());
+}
+
+
+uword Heap::EndAddress() {
+  return reinterpret_cast<uword>(new_space_->EndAddress());
+}
+
+
 void Heap::Init(Isolate* isolate) {
   ASSERT(isolate->heap() == NULL);
   Heap* heap = new Heap();
@@ -120,22 +167,6 @@ bool Heap::Verify() const {
 }
 
 
-void Heap::IterateOldPointers(ObjectPointerVisitor* visitor) {
-  old_space_->VisitObjectPointers(visitor);
-  code_space_->VisitObjectPointers(visitor);
-}
-
-
-uword Heap::TopAddress() {
-  return reinterpret_cast<uword>(new_space_->TopAddress());
-}
-
-
-uword Heap::EndAddress() {
-  return reinterpret_cast<uword>(new_space_->EndAddress());
-}
-
-
 #if defined(DEBUG)
 NoGCScope::NoGCScope() : StackResource(Isolate::Current()) {
   isolate()->IncrementNoGCScopeDepth();
diff --git a/runtime/vm/heap.h b/runtime/vm/heap.h
index 796cdd8c8fa..467da2f5556 100644
--- a/runtime/vm/heap.h
+++ b/runtime/vm/heap.h
@@ -53,19 +53,24 @@ class Heap {
   bool Contains(uword addr) const;
   bool CodeContains(uword addr) const;
 
-  // Initialize the heap and register it with the isolate.
-  static void Init(Isolate* isolate);
-
-  // Verify that all pointers in the heap point to the heap.
-  bool Verify() const;
-
+  // Visit all pointers in the space.
+  void IterateNewPointers(ObjectPointerVisitor* visitor);
   void IterateOldPointers(ObjectPointerVisitor* visitor);
 
+  void CollectGarbage(Space space);
+  void CollectAllGarbage();
+
   // Accessors for inlined allocation in generated code.
   uword TopAddress();
   uword EndAddress();
   static intptr_t new_space_offset() { return OFFSET_OF(Heap, new_space_); }
 
+  // Initialize the heap and register it with the isolate.
+  static void Init(Isolate* isolate);
+
+  // Verify that all pointers in the heap point to the heap.
+  bool Verify() const;
+
  private:
   Heap();
 
diff --git a/runtime/vm/heap_test.cc b/runtime/vm/heap_test.cc
index cba6e43f61c..5fb3a9628bc 100644
--- a/runtime/vm/heap_test.cc
+++ b/runtime/vm/heap_test.cc
@@ -2,4 +2,31 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-// TODO(iposva): Intentionally left blank for now.
+#include "vm/assert.h"
+#include "vm/globals.h"
+#include "vm/heap.h"
+#include "vm/unit_test.h"
+
+namespace dart {
+
+#if defined(TARGET_ARCH_IA32)
+TEST_CASE(OldGC) {
+  const char* kScriptChars =
+  "class HeapTester {\n"
+  "  static void main() {\n"
+  "    return [1, 2, 3];\n"
+  "  }\n"
+  "}\n";
+  Dart_Handle lib = TestCase::LoadTestScript(kScriptChars, NULL);
+  Dart_Handle result = Dart_InvokeStatic(lib,
+                                         Dart_NewString("HeapTester"),
+                                         Dart_NewString("main"),
+                                         0, NULL);
+
+  EXPECT_VALID(result);
+  Isolate* isolate = Isolate::Current();
+  Heap* heap = isolate->heap();
+  heap->CollectGarbage(Heap::kOld);
+}
+#endif  // TARGET_ARCH_IA32
+}
diff --git a/runtime/vm/pages.cc b/runtime/vm/pages.cc
index 62894a76d55..24c8da5a307 100644
--- a/runtime/vm/pages.cc
+++ b/runtime/vm/pages.cc
@@ -5,6 +5,7 @@
 #include "vm/pages.h"
 
 #include "vm/assert.h"
+#include "vm/gc_marker.h"
 #include "vm/object.h"
 #include "vm/virtual_memory.h"
 
@@ -55,7 +56,9 @@ PageSpace::PageSpace(Heap* heap, intptr_t max_capacity, bool is_executable)
       max_capacity_(max_capacity),
       capacity_(0),
       in_use_(0),
-      is_executable_(is_executable) { }
+      count_(0),
+      is_executable_(is_executable),
+      sweeping_(false) { }
 
 
 PageSpace::~PageSpace() {
@@ -174,4 +177,31 @@ void PageSpace::VisitObjectPointers(ObjectPointerVisitor* visitor) const {
   }
 }
 
+
+void PageSpace::MarkSweep() {
+  // MarkSweep is not reentrant. Make sure that is the case.
+  ASSERT(!sweeping_);
+  sweeping_ = true;
+  Isolate* isolate = Isolate::Current();
+  NoHandleScope no_handles(isolate);
+
+  Timer timer(FLAG_verbose_gc, "MarkSweep");
+  timer.Start();
+
+  // Mark all reachable old-gen objects.
+  GCMarker marker(heap_);
+  marker.MarkObjects(isolate, this);
+
+  UNIMPLEMENTED();
+  timer.Stop();
+  if (FLAG_verbose_gc) {
+    OS::PrintErr("Mark-Sweep[%d]: %dus\n", count_, timer.TotalElapsedTime());
+  }
+
+  count_++;
+  // Done, reset the marker.
+  ASSERT(sweeping_);
+  sweeping_ = false;
+}
+
 }  // namespace dart
diff --git a/runtime/vm/pages.h b/runtime/vm/pages.h
index 6e47a98811e..18e4b604df8 100644
--- a/runtime/vm/pages.h
+++ b/runtime/vm/pages.h
@@ -85,6 +85,9 @@ class PageSpace {
 
   void VisitObjectPointers(ObjectPointerVisitor* visitor) const;
 
+  // Collect the garbage in the page space using mark-sweep.
+  void MarkSweep();
+
  private:
   static const intptr_t kAllocatablePageSize = kPageSize - sizeof(HeapPage);
 
@@ -105,8 +108,14 @@ class PageSpace {
   intptr_t capacity_;
   intptr_t in_use_;
 
+  // Old-gen GC cycle count.
+  int count_;
+
   bool is_executable_;
 
+  // Keep track whether a MarkSweep is currently running.
+  bool sweeping_;
+
   DISALLOW_IMPLICIT_CONSTRUCTORS(PageSpace);
 };
 
diff --git a/runtime/vm/vm_sources.gypi b/runtime/vm/vm_sources.gypi
index 3c31ef814fe..b163ae2557a 100644
--- a/runtime/vm/vm_sources.gypi
+++ b/runtime/vm/vm_sources.gypi
@@ -103,6 +103,8 @@
     'flags.cc',
     'flags.h',
     'flags_test.cc',
+    'gc_marker.cc',
+    'gc_marker.h',
     'gdbjit_linux.cc',
     'gdbjit_linux.h',
     'globals.h',