Despite its well recognized importance, user participation in information systems development (ISD) is often limited, passive, symbolic, or marginal in practice. Users are thought to be in a weak position to influence the process and outcome of ISD. As an exploratory case study, this research reports on a refreshing user participation experience to examine what kinds of user behavior can exert strong control over ISD and how. In developing a core business system for a large commercial bank, a group of business experts collocated with the developers as part of the development team. Results show that strong control by users was achieved through their end-toend participation, which was instrumental for ISD success in terms of high quality and smooth rollout. In particular, users’ influence was strengthened over time through their participation by doing in completing some of the key tasks usually done by the IS staff. This research contributes toward a new theory on user participation from a control perspective.