Web applications are vital components of the global information infrastructure, and it is important to ensure their dependability. Many techniques and tools for validating Web applications have been created, but few of these have addressed the need to test Web application functionality and none have attempted to leverage data gathered in the operation of Web applications to assist with testing. In this paper, we present several techniques for using user session data gathered as users operate Web applications to help test those applications from a functional standpoint. We report results of an experiment comparing these new techniques to existing white-box techniques for creating test cases for Web applications, assessing both the adequacy of the generated test cases and their ability to detect faults on a point-of-sale Web application. Our results show that user session data can be used to produce test suites more effective overall than those produced by the white-box techniques considered; however, the faults detected by the two classes of techniques differ, suggesting that the techniques are complementary.