The West of Scotland Coronary Prevention Study (WOSCOPS) is a randomized, double-blind, placebo-controlled trial of pravastatin in a primary prevention context. The primary end point of the trial is definite coronary artery disease (CAD) death and/or nonfatal acute myocardial infarction. This study describes the baseline characteristics of the trial recruits and of the subjects who were screened during the recruitment process; 6,595 men, aged 45 to 64 years, with raised cholesterol levels, were randomized in equal numbers to placebo or pravastatin after initial screening of approximately 81,000 subjects in the West of Scotland. With the exception of cholesterol levels and history of CAD, the recruits had a similar risk factor profile and demographic distribution to the group of screenees from which they were selected. Compared with previous primary prevention studies of cholesterol-lowering drugs, the WOSCOPS recruits are, on average, 7 to 9 years older than subjects in other trials and have average total cholesterol levels 0.5 mmol/L (19.4 mg/dl) lower than those in the Helsinki Heart Study and the Lipid Research Clinics-Coronary Primary Prevention Trial. The study has achieved its initial goal of accumulating > 30,000 patient-years of randomized follow-up. Recruits had their final trial visits in the first half of 1995 and the main results will be available in the fourth quarter of 1995.