The effect of simvastatin on serum total and HDL cholesterol and total triglyceride levels in 20 hypercholesterolemic patients on CAPD treatment was studied. The drug was given at the initial dose of 10 mg/day which was doubled up to 40 mg/day. Two non-compliant patients stopped the drug in the first week of treatment. One patient had vomiting and stopped simvastatin. One patients reduced the dose from 20 to 10 mg/day because of increase in CPK level. The study was completed in 16 patients. Serum cholesterol decreased from 318 +/- 39 to 208 +/- 34 mg/dl (p < 0.001), triglyceride from 317 +/- 129 to 278 +/- 160 mg/dl and HDL cholesterol from 43 +/- 13 to 35 +/- 11 mg/dl. The effective does was 10 mg/day in 4 cases, 20 mg/dl in 7 and 40 mg/dl in 5. In CAPD patients, simvastatin is safe and effective in lowering serum cholesterol. The clinical significance of the decrease in HDL cholesterol and its possible effect on clinical outcome are still unknown.