Recruitment of the 3,806 CPPT subjects was completed in July 1976. After randomization into the study, each subject visited his clinic at bimonthly intervals. At these visits, adherence to drug and diet were assessed, the study medication was supplied, general health and potential toxic side effects were monitored, and intervening cardiovascular events were recorded. Counseling in drug and dietary adherence were given at each visit, and medical advice was given when a problem was identified. Trial data were collected and analyzed at the Central Patient Registry and reviewed periodically by a Safety and Data Monitoring Board. Intervention ceased between May and August 1983. A five-year follow-up was initiated in November 1984 to detect possible toxicity in the CPPT participants following ingestion of cholestyramine (or placebo) for 7 to 10 years. Follow-up was completed in October 1989.