Similar general medical outpatient clinics with randomly assigned patients were used to evaluate the effectiveness of a program that was to increase house staff compliance with preventive medicine guidelines. Two clinics were designated experimental and two served as controls. In the experimental clinics, age-specific checklists of all recommended preventive procedures (drawn from the Canadian Task Force report on The Periodic Health Examination and American Cancer Society guidelines) were appended to each patient's chart. In addition, house officers were presented with a series of weekly seminars dealing with issues in screening, as well as the specific recommendations included in the checklist. House officers in all four clinics were tested for their knowledge and attitudes toward the preventive program before and after the intervention. Counts of immunizations and mammograms performed and the total populations eligible for these procedures were determined for all four clinics. As predicted, test scores as well as mammography and immunization rates increased significantly (from 2-40 per cent) in the intervention clinics as compared with controls. We conclude that this intervention was clearly effective in the short run. However, follow-up studies will be necessary to determine whether the desired long-term effect has been achieved.