The protocol for the trial was approved in November 1972. Beginning in July 1973, men with hypercholesterolemia were recruited as potential trial subjects from such diverse sources as physician referrals, blood bank donor lists, and mass screening programs. Each subject was screened further in a series of four visits, the purpose of which was to select only men (1) whose lipid abnormality was of the primary Type II phenotype, (2) who were free of clinically manifest coronary heart disease, and (3) whose excellent overall health and reliability made 7-10 years of follow-up a realistic objective. Additionally, a standardized limited-cholesterol/saturated fat diet was initiated at the second of these visits in order to exclude men whose cholesterol levels were highly responsive to diet. Subjects who met all the selection criteria were randomly assigned, in a double-blind fashion, to receive either the cholesterol-lowering drug cholestyramine or a placebo at their fifth visit.