DXplain, a computer-based medical education, reference and decision support system has been used by thousands of physicians and medical students on stand-alone systems and over communications networks. For the past two years, we have made DXplain available over the Internet in order to provide DXplain's knowledge and analytical capabilities as a resource to other applications within Massachusetts General Hospital (MGH) and at outside institutions. We describe and provide the user experience with two different protocols through which users can access DXplain through the World Wide Web (WWW). The first allows the user to have direct interaction with all the functionality of DXplain where the MGH server controls the interaction and the mode of presentation. In the second mode, the MGH server provides the DXplain functionality as a series of services, which can be called independently by the user application program.