diff --git a/libtbx/test_utils/__init__.py b/libtbx/test_utils/__init__.py
index 4d30be6d03..91743611ef 100644
--- a/libtbx/test_utils/__init__.py
+++ b/libtbx/test_utils/__init__.py
@@ -913,6 +913,35 @@ def exercise():
   assert precision_approx_equal(0.799999,0.800004,precision=18)==False
   print("OK")
 
+def iterate_tests_without_and_with_mmCIF_conversion():
+  """ Return a simple iterator that first does nothing and returns False,
+      then converts all pdb_str_xxxx locals to mmCIF-only format
+      and prints a notice and returns True.
+
+      Behavior can be modified by specifying "skip_mmcif" or "mmcif_only"
+       in sys.argv or by setting the value of the environmental
+      variable REGRESSION_SKIP_CIF ( mmcif_only, skip_mmcif,
+       blank or missing is run both)
+  """
+  skip_string = os.environ.get("REGRESSION_SKIP_CIF",None)
+  if skip_string is None:
+    if 'mmcif_only' in sys.argv:
+      skip_string = 'mmcif_only'
+    elif 'skip_mmcif' in sys.argv:
+      skip_string = 'skip_mmcif'
+
+  if skip_string in [None, '']:
+    run_list = [False, True]
+  elif skip_string == 'mmcif_only':
+    run_list = [True]
+  elif skip_string == 'skip_mmcif':
+    run_list = [False]
+  else:
+    raise Sorry(
+      "Unrecognized value of REGRESSION_SKIP_CIF: '%s'" %(skip_string))
+
+  return run_list
+
 def convert_pdb_to_cif_for_pdb_str(locals, chain_addition = "ZXLONG",
    key_str="pdb_str", hetatm_name_addition = "ZY", print_new_string = True):
   #  Converts all the strings that start with "pdb_str" from PDB to mmcif
diff --git a/mmtbx/regression/tst_minimize_chain.py b/mmtbx/regression/tst_minimize_chain.py
index ffbe511d9b..16e224db70 100644
--- a/mmtbx/regression/tst_minimize_chain.py
+++ b/mmtbx/regression/tst_minimize_chain.py
@@ -636,32 +636,35 @@ def tst_02(args,prefix=None):
   return rmsd
 
 if (__name__ == "__main__"):
-  for mmcif in [False, True]:
+  t0=time.time()
+  from libtbx.test_utils import iterate_tests_without_and_with_mmCIF_conversion
+  for mmcif in iterate_tests_without_and_with_mmCIF_conversion():
     if mmcif:
       from libtbx.test_utils import convert_pdb_to_cif_for_pdb_str
       convert_pdb_to_cif_for_pdb_str(locals())
       print(80*"-")
       print("RERUNNING WITH MMCIF")
       print(80*"-")
-    t0=time.time()
+
     print("\nRunning merge_models alone")
+    t0a=time.time()
     rmsd=tst_01()
-    print("Time: %6.4f"%(time.time()-t0))
+    print("Time: %6.4f"%(time.time()-t0a))
     print("OK")
 
     args=["number_of_build_cycles=2","number_of_macro_cycles=1","number_of_trials=2","random_seed=77141"]
-    t0=time.time()
+    t0a=time.time()
     print("Running standard minimize_chain")
     extra_args=['merge_models=False','pdb_out=std.pdb']
     rmsd=tst_02(args+extra_args,prefix='tst_02')
-    print("Time: %6.4f"%(time.time()-t0))
-    print("OK")
     print("RMSD %7.2f "%rmsd)
+    print("Time: %6.4f"%(time.time()-t0a))
 
-    t0=time.time()
+    t0a=time.time()
     print("\nRunning standard minimize_chain plus merge_models")
     extra_args=['merge_models=True','pdb_out=merged.pdb']
     rmsd=tst_02(args+extra_args,prefix='tst_03')
-    print("Time: %6.4f"%(time.time()-t0))
-    print("OK")
     print("RMSD %7.2f "%rmsd)
+    print("Time: %6.4f"%(time.time()-t0a))
+  print("Total Time: %6.4f"%(time.time()-t0))
+  print("OK")