A cooperative study between the University of Southern California Division of Research in Medical Education and the American College of Obstetricians and Gynecologists represents one subset of a large-scale study of manpower supply in obstetrics-gynecology. A stratified random sample of all obstetrician-gynecologists was obtained from the AMerican Medical Association's "Master File of Physicians." A total of 879 respondents (56 per cent of the sample) completed a detailed, one-week log of practice activities and self-descriptive questionnaire. This initial report describes these physicians by practice arrangement as related to age and geography. Practice work load is identified by encounter time per patient, work hours per day and week, and variations related to geographic location and population served. The descriptive findings may have important implications for manpower planning.