Simavastatin (MK-733, Zocor, CAS 79902-63-9), a new 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase inhibitor, was administered for a period of at least 3 years to 21 patients suffering from primary hypercholesterolemia. Significant decreases were noted for plasma cholesterol (30%), low density lipoprotein cholesterol (40%), whereas an increase in plasma high density lipoprotein cholesterol (11%) was observed. The drug therapy was well tolerated and clinical examinations revealed no adverse effects. No development of cataracts or other ocular side effects have been observed during this 3-year follow-up period.