One of the deliverables of the HOLON (Health Object Library Online) project is the specification of a reference architecture for clinical information systems that facilitates the development of a variety of discrete, reusable software components. One of the challenges facing the HOLON consortium is determining what kinds of components can be made available in a library for developers of clinical information systems. To further explore the use of component architectures in the development of reusable clinical subsystems, we have incorporated ongoing work in the development of enterprise terminology services into a Problem List subsystem for the HOLON testbed. We have successfully implemented a set of components using CORBA (Common Object Request Broker Architecture) and Java distributed object technologies that provide a functional problem list application and UMLS-based "Problem Picker." Through this development, we have overcome a variety of obstacles characteristic of rapidly emerging technologies, and have identified architectural issues necessary to scale these components for use and reuse within an enterprise clinical information system.