The aim of our study was the biochemical and functional examination of the liver during the therapy of familiar hyperlipoproteinemia by means of MevacorR (lovostatine) in comparison with the treatment by Vasosan S (cholestyramine). We examined 20 patients treated with a daily dose of MevacorR being 20-40 mg and, 18 patients treated with a daily dose of Vasosan S being 16-32 g for the period of 12 weeks. During the therapy the total cholesterol, LDL-cholesterol, HDL-cholesterol, triacylglycerols, hepatic enzymes (AST, ALT, ALP) activity, functional test of the liver, biological half-time of antipyrine (t 1/2 antipyrine) were investigated at the onset and at the end of the study. We discovered that at the end of the treatments by MevacorR and Vasosan S the hypolipidemic effect increased (cholesterol p < 0.001, LDL cholesterol p < 0.001), and there was difference in the effect on HDL-cholesterol and in that on triacylglycerols. During the treatment we discovered that due to both medicaments the liver enzymes activity increased to a different extent. At the beginning of the study the antipyrine biological half-time statistically increased in both investigated groups, namely in comparison with the control group. At the end of the treatments in both groups the antipyrine half-time was prolonged, however not significantly. Prior to long-term therapy by hypolipidemics the authors recommend biochemical and functional examination of the liver. (Tab. 4, Fig. 8, Ref. 7.)