The investigations have shown that the synthetic antioxidant fenbutol can be classified as one of the drugs that are effective in reducing cholesterol levels in patients with Types IIa and IIb hypercholesterolemia and a good subjective tolerance. The use of the drug along with an adequate hypolipidemic diet caused a significant decrease in total cholesterol at month 3 of therapy (on an average by 23.7%) and atherogenic low density lipoproteins (on an average by 24.6%). The level of high density lipoproteins was decreased on an average by 18.8%. The level of plasma triglycerides was changed to a lesser extent (a 13.8% decrease). The controls who took placebo showed no significant changes in lipid metabolism.