The growth of the Internet, and in particular the World Wide Web, is already influencing the way science is taught, and it will undoubtedly do so to a greater extent in the future. One important facet of this influence is the development of Web-based assessment and testing systems. These systems also provide a valuable new tool to the education research community: a tool that combines the ability of multiple-choice diagnostic tests to handle large numbers of subjects with some of the greater flexibility and additional information that other methods offer. On the other hand, some of the particular strengths of this tool also give rise to some unique disadvantages. In this article, the authors discuss the strengths and weaknesses for education research and present some suggestions for the tool's use.