Thirty five patients with cardiovascular diseases and hypercholesterolemia were treated with probucol and a low-fat diet for 12 to 50 months. The mean serum cholesterol level decreased from 327,2 to 279,4 mg/dl (- 14,6% p. < 0,001). Probucol lowered the plasma cholesterol level by about the same extent in primary hypercholesterolemia type IIa (10 patients) and in combined hypercholesterolemia type IIb or III (23 patients). No interaction was observed between probucol and other drugs prescribed for cardiovascular diseases particularly antivitamin K and diuretics. No variation in liver and renal function tests, in glucose level, blood count or body weight were noted. The E.C.G. was not modified by treatment. The therapy was withdrawn in one patient because of diarrhea.