Electronic modes of data collection and data dissemination pose challenges to instrument designers and user-interface designers (cf. Sweet & Russell, 1996). Just as ensuring the usability of a paper instrument requires cognitive testing, ensuring the usability of an electronic instrument requires usability testing. Both cognitive testing and usability testing have their roots in cognitive psychology and its findings on human thought processes. Whether the user is providing data or retrieving data, the relative usability of different user interfaces varies with the cognitive demands placed on the user, the level of consistency with user expectations, and the relative visibility of relationships between user actions and system behaviors. Examples of usability issues in a Web-based data-collection instrument and a Web-based data-dissemination tool illustrate obstacles to achieving the goal of user-centered design. Recommendations for resolving such obstacles are based on recent usability testing.