There is growing interest in the use of practice guidelines for physicians as a means of reducing inappropriate care, controlling geographic variations in practice patterns, and making more effective use of health care resources. Recent developments at the national health policy level suggest that practice guidelines will play an increasingly prominent role in the practice of medicine. The federal government has created a new US Public Health Service agency with responsibility for practice guidelines. Guidelines have been developed by more than 35 physician organizations and specialty societies. The American Medical Association and the Council of Medical Specialty Societies have endorsed practice guidelines and are organizing specialty societies to set policy on the subject. Academic medical centers have formed a research consortium on practice guidelines. Independent research centers (eg, the RAND Corporation and the Institute of Medicine) are developing methods for assessing appropriateness and setting guidelines. Other groups, such as hospitals, insurers, managed care plans, and private enterprises, are also directly involved. The implications of these developments are far reaching.