3-Hydroxy-3-methylglutaryl coenzyme A reductase inhibitors, a new class of hypolipidaemic agents, have been recently shown to be effective in lowering both total and low-density lipoprotein (LDL)-cholesterol. In the present study 20 patients were treated with simvastatin for six months. Various dosing regimens of 10, 20, and 40 mg/day were employed. Administration of simvastatin 10 to 40 mg/day resulted in a 24.7 to 35.8% reduction in LDL-cholesterol levels and in a 19.5 to 26.9% decrease of total cholesterol levels. Moreover, simvastatin increased high-density lipoprotein-cholesterol and induced a decrease in plasma triglycerides. The side-effect profile was similar to other observations and included reversible transaminase elevations, myalgia and gastrointestinal complaints. From the present study simvastatin seems to be well tolerated in the short- to medium-term and to be effective; however, its long-term tolerability needs to be confirmed.