Workflow systems and object-oriented technology have undoubtedly been some of the most important domains of interest of information technology over the past decade. Both domains however, have largely evolved independently, and not much research can be found in which workflow modeling principles and concepts have been applied to OO systems development or vice versa. In this paper, we show how the two domains can be integrated. By integrating both domains, business process modeling can benefit from the advantages of the object-oriented approach. On the other hand, a more process-oriented approach to OO development would enhance the organizational fit of object-oriented information systems development. The architecture that results from this integration is a tier-based one with a separate tier for workflow aspects.