A project to improve physician performance in colorectal cancer screening was evaluated as part of an ambulatory quality assurance program. A minimum standard was adopted requiring a digital examination and stool test for occult blood at annual check-ups of patients aged 40 years and older. During a 31/2-year period, three different intervention strategies for improved compliance with the standard were sequentially implemented and assessed: educational meeting, retrospective feedback of group compliance rate, and retrospective feedback of individual compliance rate compared with that of peers. A pretest/posttest design was employed in evaluating the first two intervention strategies. Neither strategy resulted in significant improvement in compliance. Monthly feedback of individual performance ranked with that of peers was then implemented in a randomized clinical trial utilizing a crossover design. During the first 6-month period, the physicians receiving feedback (group 1) improved from 66.0% to 79.9% (P less than 0.001), while the control group (group 2) also improved, from 67.5% to 76.6% (P less than 0.001), suggesting a spillover effect. During the second 6-month period, group 2 received feedback and group 1 did not. Group 1 stabilized at approximately 80% while group 2 continued to improve from 76.6% to 84.0% (P less than 0.001). Behavior changes persisted at 6 and 12 months after intervention.