Political, legal, ethical, social, economic, and technological changes in the twentieth century have produced a profound effect on the health care and health status of Americans and the way in which physicians and patients communicate. In the latter half of this century, the responsibility for individual health care has shifted from a physician-oriented, paternalistic approach to a patient-centered one. Patients now assume two identities: health consumers and active participants in the medical decision-making process. This phenomenon has created an environment where consumer demand for information has shifted from a single focus on symptoms, diagnosis, and treatment of diseases to an increasing preoccupation with cost, quality, and access to health care. This shift emphasizes the critical role played by medical librarians in the dissemination of needed information, and it challenges librarians to take a leadership role in opening newer channels of communication between physicians and patients. The 1992 Janet Doe Lecture analyzes the evolutionary change in the physician-patient relationship and its modes of communication, projects future roles for medical librarians, and provides an extensive list of references for further reading.