Methods to produce change in physician practice patterns are of increasing importance to payers and regulators as well as to physicians themselves. Because some of the strategies being adopted occur without physician input and participation, they have aroused concern in the medical community. We describe the methods used and results achieved by the Maine Medical Assessment Foundation, a nonprofit education and research organization, that has been active in practice pattern analysis since the late 1970s. The foundation has successfully engaged clinicians in a program of systematic assessment of medical care provided to residents of Maine. Significant change in practice patterns has been documented. Physicians have become active participants in the process of voluntary self-assessment, education, and quality improvement.