diff --git a/mps/src/amcssth.c b/mps/src/amcssth.c
new file mode 100644
index 00000000000..2a5bf0aa00a
--- /dev/null
+++ b/mps/src/amcssth.c
@@ -0,0 +1,249 @@
+/* impl.c.amcss: POOL CLASS AMC STRESS TEST
+ *
+ * $HopeName: MMsrc!amcss.c(trunk.30) $
+ * Copyright (C) 2000 Harlequin Ltd.  All rights reserved.
+ */
+
+#define _POSIX_C_SOURCE 199309L
+
+#include "fmtdy.h"
+#include "testlib.h"
+#include "mpscamc.h"
+#include "mpsavm.h"
+#include "mpstd.h"
+#ifdef MPS_OS_W3
+#include "mpsw3.h"
+#endif
+#include "mps.h"
+#ifdef MPS_OS_SU
+#include "ossu.h"
+#endif
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <assert.h>
+#include <pthread.h>
+#include <time.h>
+
+
+#define testArenaSIZE     ((size_t)64<<20)
+#define avLEN             3
+#define exactRootsCOUNT   300
+#define ambigRootsCOUNT   50
+#define collectionsCOUNT  18
+#define rampSIZE          5
+#define initTestFREQ      6000
+/* objNULL needs to be odd so that it's ignored in exactRoots. */
+#define objNULL           ((mps_addr_t)0xDECEA5ED)
+
+static mps_pool_t pool;
+static mps_ap_t ap;
+static mps_addr_t exactRoots[exactRootsCOUNT];
+static mps_addr_t ambigRoots[ambigRootsCOUNT];
+
+
+static mps_addr_t make(void)
+{
+  size_t length = rnd() % (2*avLEN);
+  size_t size = (length+2) * sizeof(mps_word_t);
+  mps_addr_t p;
+  mps_res_t res;
+
+  do {
+    MPS_RESERVE_BLOCK(res, p, ap, size);
+    if(res)
+      die(res, "MPS_RESERVE_BLOCK");
+    res = dylan_init(p, size, exactRoots, exactRootsCOUNT);
+    if(res)
+      die(res, "dylan_init");
+  } while(!mps_commit(ap, p, size));
+
+  return p;
+}
+
+
+static void test_stepper(mps_addr_t object, void *p, size_t s)
+{
+  (*(unsigned long *)p)++;
+  testlib_unused(s);
+  testlib_unused(object);
+}
+
+
+static void *test(void *arg, size_t s)
+{
+  mps_arena_t arena;
+  mps_fmt_t format;
+  mps_root_t exactRoot, ambigRoot;
+  unsigned long objs; size_t i;
+  mps_word_t collections, rampSwitch;
+  mps_alloc_pattern_t ramp = mps_alloc_pattern_ramp();
+  int ramping;
+  mps_ap_t busy_ap;
+  mps_addr_t busy_init;
+
+  arena = (mps_arena_t)arg;
+  (void)s; /* unused */
+
+  die(dylan_fmt(&format, arena), "fmt_create");
+
+  die(mps_pool_create(&pool, arena, mps_class_amc(), format),
+      "pool_create(amc)");
+
+  die(mps_ap_create(&ap, pool, MPS_RANK_EXACT), "BufferCreate");
+  die(mps_ap_create(&busy_ap, pool, MPS_RANK_EXACT), "BufferCreate");
+
+  for(i=0; i<exactRootsCOUNT; ++i)
+    exactRoots[i] = objNULL;
+  for(i=0; i<ambigRootsCOUNT; ++i)
+    ambigRoots[i] = (mps_addr_t)rnd();
+
+  die(mps_root_create_table_masked(&exactRoot, arena,
+                                   MPS_RANK_EXACT, (mps_rm_t)0,
+                                   &exactRoots[0], exactRootsCOUNT,
+                                   (mps_word_t)1),
+      "root_create_table(exact)");
+  die(mps_root_create_table(&ambigRoot, arena,
+                            MPS_RANK_AMBIG, (mps_rm_t)0,
+                            &ambigRoots[0], ambigRootsCOUNT),
+      "root_create_table(ambig)");
+
+  /* create an ap, and leave it busy */
+  die(mps_reserve(&busy_init, busy_ap, 64), "mps_reserve busy");
+
+  collections = 0;
+  rampSwitch = rampSIZE;
+  mps_ap_alloc_pattern_begin(ap, ramp);
+  mps_ap_alloc_pattern_begin(busy_ap, ramp);
+  ramping = 1;
+  objs = 0;
+  while(collections < collectionsCOUNT) {
+    unsigned long c;
+    size_t r;
+
+    c = mps_collections(arena);
+
+    if(collections != c) {
+      collections = c;
+      printf("\nCollection %lu, %lu objects.\n",
+             c, objs);
+      for(r = 0; r < exactRootsCOUNT; ++r)
+        assert(exactRoots[r] == objNULL ||
+               dylan_check(exactRoots[r]));
+      if(collections == collectionsCOUNT / 2) {
+        unsigned long object_count = 0;
+        mps_arena_park(arena);
+	mps_amc_apply(pool, test_stepper, &object_count, 0);
+	mps_arena_release(arena);
+	printf("mps_amc_apply stepped on %lu objects.\n", object_count);
+      }
+      if(collections == rampSwitch) {
+        rampSwitch += rampSIZE;
+        if(ramping) {
+          mps_ap_alloc_pattern_end(ap, ramp);
+          mps_ap_alloc_pattern_end(busy_ap, ramp);
+          /* Every other time, switch back immediately. */
+          if(collections & 1) ramping = 0;
+        }
+        if(!ramping) {
+          mps_ap_alloc_pattern_begin(ap, ramp);
+          mps_ap_alloc_pattern_begin(busy_ap, ramp);
+          ramping = 1;
+        }
+      }
+    }
+
+    r = rnd();
+    if(r & 1) {
+      i = (r >> 1) % exactRootsCOUNT;
+      if(exactRoots[i] != objNULL)
+        assert(dylan_check(exactRoots[i]));
+      exactRoots[i] = make();
+      if(exactRoots[(exactRootsCOUNT-1) - i] != objNULL)
+        dylan_write(exactRoots[(exactRootsCOUNT-1) - i],
+                    exactRoots, exactRootsCOUNT);
+    } else {
+      i = (r >> 1) % ambigRootsCOUNT;
+      ambigRoots[(ambigRootsCOUNT-1) - i] = make();
+      /* Create random interior pointers */
+      ambigRoots[i] = (mps_addr_t)((char *)(ambigRoots[i/2]) + 1);
+    }
+
+    if(r % initTestFREQ == 0)
+      *(int*)busy_init = -1; /* check that the buffer is still there */
+
+    if(objs % 1024 == 0) {
+      putchar('.');
+      fflush(stdout);
+    }
+
+    ++objs;
+  }
+
+  (void)mps_commit(busy_ap, busy_init, 64);
+  mps_ap_destroy(busy_ap);
+  mps_ap_destroy(ap);
+  mps_root_destroy(exactRoot);
+  mps_root_destroy(ambigRoot);
+  mps_pool_destroy(pool);
+  mps_fmt_destroy(format);
+
+  return NULL;
+}
+
+
+static void *fooey2(void *arg, size_t s)
+{
+  #if 0
+  struct timeval now;
+  int wake_sec;
+  gettimeofday(&now, NULL);
+  wake_sec = now.tv_sec + 20;
+  do {
+    sleep(1);
+    gettimeofday(&now, NULL);
+  } while (wake_sec > now.tv_sec);
+  #endif
+
+  struct timespec req, rem;
+  req.tv_sec = 10;
+  req.tv_nsec = 0;
+  while(nanosleep(&req, &rem))
+    req = rem;
+  return arg;
+}
+
+static void *fooey(void *arena)
+{
+  void *r;
+  mps_thr_t thread;
+  mps_thr_t thread2;
+  /* register the thread twice, just to make sure it works */
+  die(mps_thread_reg(&thread, (mps_arena_t)arena), "thread_reg");
+  die(mps_thread_reg(&thread2, (mps_arena_t)arena), "thread2_reg");
+  mps_tramp(&r, fooey2, (mps_arena_t)arena, 0);
+  mps_thread_dereg(thread);
+  mps_thread_dereg(thread2);
+  return r;
+}
+
+int main(void)
+{
+  mps_arena_t arena;
+  mps_thr_t thread;
+  pthread_t pthread1;
+  void *r;
+
+  die(mps_arena_create(&arena, mps_arena_class_vm(), testArenaSIZE),
+      "arena_create\n");
+  adjust_collection_freq(0.0);
+  die(mps_thread_reg(&thread, arena), "thread_reg");
+  pthread_create(&pthread1, NULL, fooey, (void *)arena);
+  mps_tramp(&r, test, arena, 0);
+  mps_thread_dereg(thread);
+  mps_arena_destroy(arena);
+
+  fflush(stdout); /* synchronize */
+  fprintf(stderr, "\nConclusion:  Failed to find any defects.\n");
+  return 0;
+}