diff --git a/README.rst b/README.rst
index 0298897..1f247a3 100644
--- a/README.rst
+++ b/README.rst
@@ -100,6 +100,9 @@ https://tahoe-lafs.org/trac/pyutil
 tests and benchmarks
 ====================
 
+Testing requires these dependencies: ``twisted``, ``setuptools_trial``,
+and ``simplejson``.
+
 To run tests: ``python ./setup.py trial -s pyutil.test.current``.
 
 You can also run the tests with the standard pyunit test runner instead of
@@ -125,6 +128,20 @@ pyutil.test import test_cache; test_cache.slow_bench()'``
 (The "-O" is important when benchmarking, since cache has extensive
 self-tests that are optimized out when -O is included.)
 
+testing with virtualenv
+-----------------------
+
+You can install all testing tools and test-time dependencies in a local
+`virtualenv` which avoids interference with user- or system-wide python
+packages. Here's an example of this process (command output omitted):
+
+.. code:: bash
+
+    $ git clone 'https://github.com/zooko/pyutil'
+    $ cd pyutil/
+    $ virtualenv ./venv
+    $ ./venv/bin/pip install twisted setuptools_trial simplejson
+    $ ./venv/bin/python ./setup.py trial -s pyutil.test
 
 LICENCE
 =======