Lovastatin is a potent new drug for lowering serum cholesterol through inhibition of 3-hydroxy-3-methylglutaryl-coenzyme A reductase, the rate-limiting enzyme for cholesterol biosynthesis. Metabolic studies with lovastatin in healthy volunteers and patients with hypercholesterolemia suggest reduced synthesis of low-density lipoprotein cholesterol (LDL-C) as well as enhanced catabolism LDL-C mediated through LDL receptors as the principal mechanisms for lipid-lowering effects. Total cholesterol and LDL-C are reduced by 30% or more on average when added to baseline therapy, with the effects being more pronounced in nonfamilial than in familial hypercholesterolemia. Optimal dosing appears to be 20 mg given twice a day. The most common adverse effects are gastrointestinal, while the most serious are elevated transaminase levels and the potential for lens opacities. Lovastatin is the first of a new class of lipid-lowering agents, and is effective when added to diet therapy or in combination with other drugs.