Integrating functions from disparate and widely-distributed information systems has been an interest of the medical informatics community for some time. Barriers to progress have included the lack of network-accessible information sources, inadequate methods for inter-system messaging, and lack of vocabulary translation services. With the advent of the World Wide Web (WWW) and the evolution of the National Library of Medicine's Unified Medical Language System (UMLS), it is now possible to develop applications that integrate functions from diverse, distributed systems. In this paper we describe one such system, MedWeaver, a WWW application that integrates functions from a decision support application (DXplain), a literature searching system (WebMedline), and a clinical Web searching system (CliniWeb) using the UMLS Metathesaurus for vocabulary translation. This system demonstrates how application developers can design systems around anticipated clinical information needs and then draw together the needed content and functionality from diverse sources.