Fenofibrate, a phenoxyacid derivative, given at daily dose of 300mg during 1 year following a single blind design, lowered significantly serum triglycerides and total cholesterol in patients various types of hyperlipoproteinemias (IIa, IV, V), fibrate significantly reduced plasma uric acid. Side effects were few after prolonged treatment. Moderate and transient increases in creatine phosphokinase and glutamopyruvic transaminase values were shown in some patients. An interaction with oral anticoagulants was also observed.