The activities of six physician specialties that care for patients with highly similar problems were compared. Factors that influence the doctor's tendency to treat more patients and to work more hours were also assessed, along with impacts of geographic factors on service delivery. Data were obtained from the Medical Activities and Manpower Projects of the University of Southern California, and the U.S. Bureau of Health Professions' Areas Resource File of secondary data related to medical practice. The following specialties were analyzed: family practitioners, internists, cardiologists, pediatricians, orthopedic surgeons, and emergency physicians. A case-mix index was created to measure the degree to which physicians concentrated on cases typical of the work of their specialties. In addition, a severity-complexity index was formulated to indicate the seriousness of each patient's presenting condition. Inferences based on the findings include the following: raising physicians' fees is not likely to increase the supply of physicians services already in an area; and increasing the use of aides will not allow physicians to see significantly more patients. Appendices include extensive statistical tables of study findings and information on the activities of female and emergency physicians. (SW)