The four-week lipoprotein lowering effect of 0.2 g t.i.d. of BM 15.075 and of 0.5 g t.i.d. of clofibrate was studied in 29 subjects with different types of hyperlipoproteinaemia in a single blind crossover fashion. BM 15.075 decreased very low density lipoproteins (VLDL), triglycerides (TG) and cholesterol concentration in all types of hyperlipoproteinaemia the effect being dependent on initial lipoprotein concentrations. BM 15.075 decreased VLDL triglyceride concentrations on average 20% more than did clofibrate. BM 15.075 decreased low density lipoproteins (LDL) cholesterol concentrations in Type IIA and IIB but did not significantly affect this lipoprotein lipid in type IV hyperlipoproteinaemia. Regression analysis showed that the drug tended to decrease LDL cholesterol if initial concentrations were above 157 mg/100 ml and to increase initially lower levels. No significant differences between BM 15.075 and clofibrate was found in the effect of LDL cholesterol. High density lipoproteins (HDL) cholesterol concentrations were not influenced by BM 15.075. No subjective side effects were noted on BM 15.075. S-ASAT increased and alcaline phosphatases decreased on both treatments.