Pirozadil (pyridine 2,6-dimethanol-bis(3,4,5-trimethoxybenzoate), Pemix) was administered for 16 weeks at a dose of 1.5 or 2.0 g/d to 15 adults with Type IIa hyperlipidemia. All patients had achieved a stable weight and were given a diet before treatment. Plasma lipids, lipoproteins and apolipoproteins were measured at 4-week intervals. Pirozadil reduced the mean total cholesterol (TC) level from 291.0 mg/dl to 260.8 mg/dl in 16 weeks (p less than 0.05). The mean percentage decrease was 8.5% in week 16. Low density lipoprotein (LDL)-cholesterol and apolipoprotein B (apoB) decreased 9.7% and 8.5%, respectively, in week 16. A decrease of more than 10% in TC, representing a decrease of more than 30 mg/dl, was observed in 12 of the 15 patients. These 12 patients, who were regarded as responders, showed mean decreases in the levels of TC, LDL-cholesterol and apoB of 13.7%, 10.4% and 11.7%, respectively, but no significant change in the level of high density lipoprotein (HDL)-cholesterol or serum triglycerides. Eight of 11 patients in the lower dose group (1.5 g/d) and all 4 patients who had obtained the higher dose (2.0 g/d) were responders. Suspected side effects of pirozadil were edema, numbness of the extremities and palpitation. The results obtained suggest the beneficial effect of pirozadil on serum lipids in patients with Type IIa hyperlipoproteinemia.