18 patients treated at a specialized consultation centre for disorders of fat metabolism were administered a new-generation hypolipidemic (preparation lovastatin-Mevacor) produced by Merck Sharp and Dohme, which inhibits intracellular synthesis of cholesterol. The study also discusses specific types of heterozygotes with familial hypercholesterolemia representing a homogeneous group of patients with maximum resistance to medication and dietary therapy. Mevacor was administered in increasing doses of 20.40 and 80 mg daily for a three-month period. During therapy cholesterol and apolipoprotein B levels significantly decreased, the former from 10.13 to 7.19 mmol/l, the latter from 1.95 to 1.49 g/l. Protective HDL cholesterol significantly increased from 1.01 to 1.23 mmol/l without the triglyceride level indicating any significant change. The course of therapy did not result in any undesirable effects necessitating drug discontinuation. During the clinical testing the patients' weight remained unchanged.