A factorial design randomized controlled trial to test several clinically feasible strategies primary-care practitioners may use in routine practice to increase patient participation in occult blood testing for colorectal cancer is reported. Three compliance-enhancing intervention strategies (physician/nurse talk, and/or reminder postcard, and/or reminder phone call) were introduced. Patient health beliefs were examined as compliance predictors. High compliance levels were seen in all intervention groups, with a mean of 89% compared with 68% in controls. An interactive talk by the physician or nurse increased compliance by 12-13%. The reminder postcard was the most effective single intervention. It increased compliance by 24-25%, achieving 92.7% overall compliance, and appeared to be cost-effective. Patient health beliefs were of minimal value in predicting compliance in this study.