Health systems that have a strong orientation toward primary care achieve lower overall costs, better satisfaction of their populations, and better health. The role of specialists in such systems is to provide consultative services on a short-term basis (secondary care) or long-term services for rare or complicated problems (tertiary care). Among both primary-care and specialist physicians, opinions vary considerably as to the specific tasks that are appropriate in primary and specialist care. Medical education has not proved an adequate basis for judging either the relative appropriateness of care by primary-care physicians and specialists or criteria for referral. Recent studies indicate that conventional wisdom concerning the nature and treatment of disease that is derived from research in tertiary medical centers is contradicted by collaborative practice-based studies in primary care. Better collaboration between primary-care physicians and specialists both in research and in the design of services will be the key to more informed decisions about improvement in the care of patients with diabetes and other important and common health-care problems.