Lovastatin, a competitive inhibitor of the rate limiting enzyme in cholesterol biosynthesis was administered to 34 patients with primary hypertlipidemia, 20 mg once daily with the evening meal. Patients experienced mean total and LDL cholesterol reductions of 30.9% and 34.0% respectively. HDL cholesterol level was significantly increased by 15.4% and plasma triglyceride level was decreased by 11.2%. maximal hypocholesterolemic effects were evident at 8 weeks, after which the effects were stable. Adverse effects were noted in 2 patients who had mild gastrointestinal symptoms, that subsided after discontinuing the drug.