diff --git a/docs/logging-usage.rst b/docs/logging-usage.rst
index 3dd2a6efab19..e39027c5406f 100644
--- a/docs/logging-usage.rst
+++ b/docs/logging-usage.rst
@@ -13,6 +13,12 @@ Authentication and Configuration
   to interact with. If you are Google App Engine or Google Compute Engine
   this will be detected automatically.
 
+- The library now enables the ``gRPC`` transport for the logging API by
+  default, assuming that the required dependencies are installed and
+  importable.  To *disable* this transport, set the
+  :envvar:`GCLOUD_DISABLE_GAX` environment variable to a non-empty string,
+  e.g.:  ``$ export GCLOUD_DISABLE_GAX=1``.
+
 - After configuring your environment, create a
   :class:`Client <gcloud.logging.client.Client>`
 
diff --git a/docs/pubsub-usage.rst b/docs/pubsub-usage.rst
index 9a7f7e7acf27..b530fc37672d 100644
--- a/docs/pubsub-usage.rst
+++ b/docs/pubsub-usage.rst
@@ -7,6 +7,17 @@ Authentication / Configuration
 - Use :class:`Client <gcloud.pubsub.client.Client>` objects to configure
   your applications.
 
+- In addition to any authentication configuration, you should also set the
+  :envvar:`GCLOUD_PROJECT` environment variable for the project you'd like
+  to interact with. If you are Google App Engine or Google Compute Engine
+  this will be detected automatically.
+
+- The library now enables the ``gRPC`` transport for the pubsub API by
+  default, assuming that the required dependencies are installed and
+  importable.  To *disable* this transport, set the
+  :envvar:`GCLOUD_DISABLE_GAX` environment variable to a non-empty string,
+  e.g.:  ``$ export GCLOUD_DISABLE_GAX=1``.
+
 - :class:`Client <gcloud.pubsub.client.Client>` objects hold both a ``project``
   and an authenticated connection to the PubSub service.
 
diff --git a/gcloud/logging/client.py b/gcloud/logging/client.py
index 9bee2668849e..c51f502ac075 100644
--- a/gcloud/logging/client.py
+++ b/gcloud/logging/client.py
@@ -47,7 +47,8 @@
 from gcloud.logging.sink import Sink
 
 
-_USE_GAX = _HAVE_GAX and (os.environ.get('GCLOUD_ENABLE_GAX') is not None)
+_DISABLE_GAX = os.getenv('GCLOUD_DISABLE_GAX', False)
+_USE_GAX = _HAVE_GAX and not _DISABLE_GAX
 
 
 class Client(JSONClient):
diff --git a/gcloud/pubsub/client.py b/gcloud/pubsub/client.py
index e5f88ab36cb5..eb6e808872f0 100644
--- a/gcloud/pubsub/client.py
+++ b/gcloud/pubsub/client.py
@@ -41,7 +41,8 @@
 # pylint: enable=ungrouped-imports
 
 
-_USE_GAX = _HAVE_GAX and (os.environ.get('GCLOUD_ENABLE_GAX') is not None)
+_DISABLE_GAX = os.getenv('GCLOUD_DISABLE_GAX', False)
+_USE_GAX = _HAVE_GAX and not _DISABLE_GAX
 
 
 class Client(JSONClient):