We compared preventive care performed by 20 generalists and 20 subspecialists practicing in Santa Clara and San Mateo Counties, California, by auditing charts of adult primary care patients for compliance with recommendations of the Canadian Task Force on the Periodic Health Examination. Generalists and subspecialists both provided 49 per cent of recommended preventive services. The two groups did not differ significantly in performance of any individual service. Performance varied widely within both groups. Of many factors explored, only two were associated with more preventive services: provision of a complete physical examination to the patient, and a physician's belief in the importance of a given service. The "generalist vs. subspecialist" debate assumes that a physician's specialty classification is an important predictor of behavior. For the performance of preventive care, this was not true in our study. Instead, physicians' beliefs and practice habits may be major determinants of the quality of preventive care provided. These exploratory findings needed confirmation in other settings.