The arrival of social scientists on medical campuses increasingly presents medical librarians with a new kind of challenge. Since the war, the social scientists have expanded greatly in their specializations, in the amount of research published, and in the locales where social scientists work-including medical centers. Through their teaching activities and research, they will greatly affect tomorrow's medical libraries. In building social science collections, good working relations between librarians and scientists are needed. Some librarians may also need to be trained in the social sciences for their own work.