Though information systems may be available, potential users may not know enough about them to take advantage of the information stored there. The author used a case study method to assess the effectiveness of exposure to information on the Medical Literature Analysis and Retrieval System (MEDLARS) on potential users of the system at the University of Illinois. A "change agent" made a slide-script presentation on the demand/search service, the information stored in the system, retrieval methods, and a detailed explanation of ways to obtain the service. Some of those present also received a "Guide to MEDLARS Services" by mail later. An analysis of MEDLARS use showed that the presentation and mailing had a positive relationship to the number of subsequent adoptions of MEDLARS. (LS)