SummaryIn 45 patients with types IIa, IIb and IV hyperpidemias, we compared the following therapeutic sequences: diet alone (2 months), diet + clofibrate (2 months), diet + fenofibrate (2–10 months) and diet + clofibrate (2 months). Clofibrate significantly decreased both cholesterol and triglyceride levels. Fenofibrate was more active than clofibrate on both lipids values. When the patients were switched again to clofibrate, serum cholesterol levels rose significantly. As a rule, tolerance was good but we noticed occasional SGPT increases during both drugs’administration. Transient inceases of serum urea and/or creatinine levels were noted during fenofibrate administration. We con elude that procetofene is a powerful hypolipidemic agent even in patients who respond poorly to clofibrate. It seems advisable to control hepatic and renal functions before and during fenofibrate administration.