We sought the voluntary cooperation of a randomly selected sample of community physicians and hospitals in five states for a study of how appropriately they performed coronary angiography, carotid endarterectomy, and upper gastrointestinal tract endoscopy. Ninety percent of 913 sampled physicians (n = 819) consented to a review of up to 20 of their 1981 Medicare patients' records. These physicians represented seven different specialties and subspecialties and performed 4988 procedures, 92% of the desired sample. Only three of 230 hospitals did not participate. We attribute our method's success primarily to the formation of a network to connect the branches of the profession, respect for office and hospital practice routine, confidentiality, and the development of carefully designed medical record abstraction systems. We conclude that, with effort, cooperative research among disparate segments of the medical community can become a reality even if the topic studied is relatively sensitive.