The effect of CS-514 (eptastatin, Sankyo Co., Tokyo), a competitive inhibitor of 3-hydroxy-3-methylglutaryl coenzyme A reductase, was investigated in 47 patients with hypercholesterolemia (WHO type IIa: 27, IIb: 20). Ten or 20 mg of CS-514 was administered daily for 3 months. In both types of patient, total cholesterol and phospholipid levels were significantly reduced by CS-514. The triglyceride, cholesterol and phospholipid content of low density lipoprotein (LDL) and the plasma levels of apolipoprotein B were also decreased in both groups. In contrast, total triglyceride, very low density lipoprotein (VLDL)-triglyceride and apolipoprotein C-II were decreased only in type IIb subjects. Also the levels of high density lipoprotein (HDL)-cholesterol and apolipoproteins A-I and A-II were increased by CS-514 in IIb but not in IIa patients. In both groups, no change occurred in either the cholesterol/triglyceride or phospholipid ratio in any lipoprotein fraction, nor in the ratio of HDL-cholesterol to apolipoprotein A-I or A-II, respectively. Therefore, CS-514 suppresses plasma levels of cholesterol in hypercholesterolemic patients without modifying lipoprotein composition. Moreover, this drug has different effects on the levels of plasma triglyceride and HDL-cholesterol of type IIa and IIb patients.