In an academic general medicine clinic, we performed a randomized, controlled trial to compare (1) the effects of supplying monthly feedback reports of compliance with preventive care protocols by 135 internal medicine house staff with (2) the effects of specific reminders given to them at the time of patient visits. The protocols were randomly divided into two groups, A and B, and half the house staff were given feedback for Group A and half for Group B. Thus, each group served as a control for the other. Each feedback group was also randomly assigned to receive reminders for either Group A or B protocols. House staff receiving feedback more often complied with fecal occult blood testing, mammography, pneumococcal vaccination, use of metronidazole, and combined Group A and B protocols than did controls (P less than 0.01). There was also significantly more compliance with the same protocols by house staff receiving reminders, but the increase for fecal occult blood testing, pneumococcal vaccination, and combined Group A protocols was twice that seen in physicians given feedback alone. In addition, reminders alone increased compliance with oral calcium supplementation. Overall compliance with the preventive care protocols was low: 10-15% in physicians receiving neither feedback nor reminders, increasing to 15-30% in those receiving reminders. Physician compliance with suggested preventive care protocols can be increased by both delayed feedback and immediate reminders, but reminders have a greater effect.