Seven patients with hyperlipoproteinemia (HLP) type II (four patients with type II A and three patients with type II B), who were experienced to be resistant to hypolipidemic drugs, were treated for 6 months with etofibrate, a double-ester of nicotinic acid and clofibrinic acid, at a dose of 0.3 g t.i.d. Mean serum cholesterol level decreased by up to 18% from a pre-treatment value of 7.7 +/- 1.4 mmol/l. The reduction of serum cholesterol was due both to a decrease in very low density (VLDL) and low density (LDL) lipoprotein cholesteral by 61 and 25%, respectively (after 6 months). Furthermore alpha-LP (HDL) cholesterol increased by 8%, (after 6 months). All seven patients had previously received clofibrate and had obtained a mean decrease in plasma cholesterol by 6%. There was a slight transient increase in S-ASAT and S-ALAT simultaneous with in increase in serum urate. However, these values returned after 3 months to pre-treatment level. No influence on glucose tolerance was recorded. There were no bothersome side effects except a transient discomfort in the form of flushing or acid indigestion which occurred after 1--2 months of treatment with etofibrate.