The Air Force/Texas Coronary Atherosclerosis Prevention Study (AFCAPS/TexCAPS) is a randomized, double-blind, placebo-controlled primary prevention trial. It is designed to test the hypothesis that in addition to a lipid-lowering diet, treatment with lovastatin is more effective than placebo in reducing acute major coronary events (i.e., sudden cardiac death, fatal and nonfatal myocardial infarction, and unstable angina) in a cohort with normal to mildly elevated total (180 to 264 mg/dl) and low-density lipoprotein (LDL) cholesterol (130 to 190 mg/dl) and low high-density lipoprotein (HDL) cholesterol (< or =45 mg/dl for men and < or =47 mg/dl for women). Two sites in Texas, Lackland Air Force Base in San Antonio and the University of North Texas Health Science Center in Fort Worth, will conduct the study. After at least 12 weeks of an American Heart Association Step 1 diet and 2 weeks placebo run-in, 6,605 men and women, ages 45 to 73 and 55 to 73 years, respectively, without clinical evidence of coronary heart disease, are randomized in equal numbers to either lovastatin (20 mg/day) or placebo. Study procedures maintain the blind, allowing titration of lovastatin from 20 to 40 mg/day to achieve an LDL cholesterol goal of < or = 110 mg/dl. All participants are followed until study completion, when 320 participants have had a primary end point or a minimum of 5 years after the last participant is randomized, whichever occurs last. All end points are adjudicated by an independent committee using prespecified criteria. Unique features of this trial are (1) the inclusion of unstable angina in the primary end point to reflect the increasing trend to treat coronary heart disease aggressively before a myocardial infarction has occurred, (2) aggressive pharmacologic intervention, with titration, to attain an LDL cholesterol goal less than the current National Cholesterol Education Panel guidelines for primary prevention, and (3) a cohort that includes women, the elderly, and those with mild to moderate hyperlipidemia and low HDL cholesterol. Compared with earlier studies, results will be applicable to a broader population and may help clarify the role of aggressive LDL cholesterol reduction measures in primary prevention. Treatment of this population is likely to realize the greatest cumulative long-term benefit in the prevention of acute major coronary events.