diff --git a/mlflow/tracking/client.py b/mlflow/tracking/client.py
index 511efa291ab62..451336a774754 100644
--- a/mlflow/tracking/client.py
+++ b/mlflow/tracking/client.py
@@ -157,7 +157,7 @@ def rename_experiment(self, experiment_id, new_name):
         """
         self.store.rename_experiment(experiment_id, new_name)
 
-    def log_metric(self, run_id, key, value, timestamp=None):
+    def log_metric(self, run_id, key, value, timestamp=None, step=0):
         """
         Log a metric against the run ID. If timestamp is not provided, uses
         the current timestamp.
diff --git a/mlflow/tracking/fluent.py b/mlflow/tracking/fluent.py
index ced34c3fbe87b..ec03c5ff009ba 100644
--- a/mlflow/tracking/fluent.py
+++ b/mlflow/tracking/fluent.py
@@ -60,6 +60,7 @@ class ActiveRun(Run):  # pylint: disable=W0223
 
     def __init__(self, run):
         Run.__init__(self, run.info, run.data)
+        self.step = 0
 
     def __enter__(self):
         return self
@@ -186,15 +187,22 @@ def set_tag(key, value):
     MlflowClient().set_tag(run_id, key, value)
 
 
-def log_metric(key, value):
+def log_metric(key, value, step=None):
     """
     Log a metric under the current run, creating a run if necessary.
 
     :param key: Metric name (string).
     :param value: Metric value (float).
     """
-    run_id = _get_or_start_run().info.run_uuid
-    MlflowClient().log_metric(run_id, key, value, int(time.time()))
+    run = _get_or_start_run()
+    if step is None:
+        step = run.step
+    MlflowClient().log_metric(run_id=run.info.run_uuid,
+                              key=key,
+                              value=value,
+                              timestamp=int(time.time()),
+                              step=step)
+    run.step = step + 1 # Or just `step`?
 
 
 def log_metrics(metrics):