Previous studies suggest that among physicians who provide primary care, specialty training may have a marked impact on practice style, resource utilization and the costs of care. Subspecialty internists appear to use more medical resources than general internists, while family practitioners may use somewhat fewer, even after adjusting for differences in patient populations. However, studies to date have not clearly shown that these differences persist in a common practice environment, nor have they assessed total resource utilization or costs of care over time in populations of patients. This prospective study will use the automated data systems of the Kaiser Permanente Medical Care Program (KPMCP) of Northern California to examine differences in resource utilization and total costs during a one-year period (July l, 1994 - June 30, 1995) for patients (age 35 years and older) of three groups of primary care physicians (family practitioners, general internists, and subspecialty internists). It will be conducted in six KPMCP facilities where patients are routinely assigned to two of the three specialties without respect to their illnesses or complaints. Utilization measures include: inpatient care, outpatient visits (primary care, subspecialty medicine and noninternal medicine referrals), emergency room use, laboratory, pharmacy, radiology, outpatient surgery, and office procedures. Costs of each element are also available. Case-mix differences between specialties will be measured by brief medical record review in samples of 1,000 patients from each medical center. The Ambulatory Care Group (ACG) Case-mix System will be applied to all diagnoses occurring during the previous two years. Disease severity will be assessed for five key chronic conditions. Quality of care measures include: assessment of appropriateness of care using recently published guidelines for patients with diabetes, hypertension, asthma, depression and low back pain; prevention practices assessed with data from a Member Health Survey completed by nearly 20,000 members in mid-1993; and medical outcomes (avoidable hospitalizations and emergency room visits). An advisory committee of national experts on primary care has been recruited to provide input into decisions on case-mix adjustment, assessment of quality of care comparisons, and the implications of findings for a national policy on primary care.