The historical and current status of information dissemination centers and the problem of user interface are reviewed. During the past decade, the problems of technical data processing have been conquered; information dissemination has evolved from a loosely knit group of experimental centers to an organization of established centers, many operating multiple data bases. Competitive data bases are becoming available in a number of subject fields, putting the centers in a better bargaining position with the data base producers. However, on-line retrieval, resource sharing, and networking must solve the common problem of user interface before anyone or any combination of these operating modes can be really effective. Interactions between the user with his question, the intermediary (the profile code processor), and the search system with its data base are critical to continued evolution of information centers. The intermediaries will, for some time, be the most effective bridge between the users and the computer-based retrieval services. The breakthrough needed for both on-line and batch retrieval systems is the understanding, modelling, and simulation of the man-machine interfaces which are now handled by the intermediaries. (WCM)