The active metabolite of fenofibrate is fenofibric acid, which is strongly bound to serum proteins. Following a single oral dose of 300 mg fenofibrate there is a diphasic decrease in plasma levels of fenofibric acid, and most of the drug is excreted as conjugate in the urine. Following daily oral administration of 300 mg during 10 days, a state of equilibrium is obtained within 2 to 3 days and persists throughout the observation period; the mean elimination half-life and urinary excretion rate are very similar to those measured after a single dose, and the drug does not accumulate. In patients with renal insufficiency, the plasma half-life of fenofibric acid is very substantially prolonged and considerable accumulation takes place, as the compound is virtually not dialyzable. Doses of 100 mg/day produce plasma levels similar to those obtained with 300 mg/day. The lipid-lowering activity mostly affects triglycerides. Concomitant administration of colestipol has no effect on blood kinetics and urinary excretion of fenofibrate but results in very important reduction of all lipoprotein fractions.