17 patients with hyperlipoproteinemia of type 11 (9 type IIa and 8 type IIb), 4 with hyperlipoproteinemia of type IV and 1 with hyperlipoproteinemia of type V were treated for 4.6 +/- 0.7 months with the new lipid lowering agent bezafibrate in a dose of 200 mg three times daily. Bezafibrate markedly lowered total serum cholesterol and triglycerides and increased HDL-cholesterol in each of these types of hyperlipoproteinemia. These data suggest that bezafibrate may be effective in reducing the possibly atherogenic LDL- and VLDL-fractions while increasing the antiatherogenic HDL-fraction.