Family practice and primary care are rapidly achieving prominence as the foundation of a rapidly changing health care system, driven not by systematic reform but by the rapid advance of managed care. The knowledge base to support primary care practice, however, lags far behind after decades of neglect in the headlong rush toward overspecialization. The success of biomedical research in the United States in the last 50 years is due in large part to the network of tertiary care hospitals, where the specialized care of highly selected patients supports broad programs of teaching and research. There are no comparable laboratories, however, for research on the important content areas of primary care. The emergence and success of practice-based research networks over the past decade provide an important infrastructure for careful study of the health and health care phenomena that comprise primary care. Practice-based research networks have made a great deal of progress in methods development and have begun to contribute important information to the primary care knowledge base. They continue, however, to be underfunded and underdeveloped, existing on large infusions of volunteerism by the participating physicians. The study recently completed by the Institute of Medicine's Committee on the Future of Primary Care will play a critical role in promoting widespread appreciation of the gap in the scientific base necessary to support primary care practice, the need for research in primary care, and the complementary relationship of this body of research and the more traditional biomedical research that has been so well funded.