Lovastatin (mevinolin), a potent inhibitor of 3-hydroxy-3-methylglutaryl coenzyme A reductase, was investigated in a double-blind, placebo-controlled multicenter study of 101 patients with nonfamilial primary hypercholesterolemia. Dosages varied from 10 to 80 mg/d in single or divided doses. Patients receiving 40 mg twice a day experienced mean total and low-density lipoprotein cholesterol reductions of 32% and 39%, respectively. High-density lipoprotein cholesterol levels tended to rise slightly and plasma triglyceride levels were moderately decreased. Adverse effects attributable to lovastatin were infrequent and no patient was withdrawn from therapy. In this study, lovastatin was a well tolerated and effective agent for the treatment of nonfamilial hypercholesterolemia.