The authors describe how Tec-Ed designed a reference documentation usability test for the Xerox VP Series Reference Library, trained test subjects, conducted the test, and evaluated the results. This usability test experience led to two conclusions about the requirements for designing tests of reference documentation usability. First, because reference documentation is designed for information access, a usability test of such documentation needs to take into account its reference aspects. Second, usability testing of reference documentation may mean delaying the test process until very near the end of the documentation development cycle. Analysis of the test results should be speedy and should provide two kinds of recommendations: short-term recommendations, which documentation specialists can implement before the impending documentation release; and long-term results, which documentation specialists can use to plan future editions of the documentation.