Type III hyperlipoproteinemia (HLP) is characterized by elevated concentrations of plasma cholesterol and triglycerides due to an increase in atherogenic beta-very low density lipoproteins (beta-VLDL). As a consequence, affected individuals develop premature and accelerated atherosclerosis. Fibrates have been shown to be most effective in treatment of the dyslipidemia in type III HLP. However, comparative data on the efficacy of different fibrates in this disorder are very limited; to assess this further we have compared in a prospective study the hypolipidemic effects of bezafibrate (400 mg once daily) and micronised fenofibrate (200 mg once daily) in 23 patients with well-characterized type III HLP. Baseline values were obtained after 4 weeks on diet and treatment values were obtained after 12 weeks of treatment with each drug. Treatment with bezafibrate and micronised fenofibrate both resulted in significant reductions in the serum concentrations of total cholesterol (26.0% and 38.7%), VLDL cholesterol (41.5% and 54.1%) and total triglycerides (27.5% and 39.1%), as well as a significant increase in high density lipoprotein (HDL) cholesterol (15.0% and 27. 8%). Micronised fenofibrate was, however, significantly (P < 0.05) more effective in reducing serum concentrations of total cholesterol and VLDL cholesterol and increasing HDL cholesterol than was bezafibrate in the same patients.