ACTH and cortisol effects on plasma lipids were studied using TLC and were evaluated by densitometry. The effect of 50 IU of ACTH was studied in 8 healthy individuals. Free fatty acids increased after 4 h, and triglycerides and esterified cholesterol increased after 6 h. Free cholesterol levels declined after another 6 h, the decrease becoming more intense after 24 h. After 24 h lecithin declined, accompanied by an increase of lysolecithin. There was a decrease in total phospholipids. Seven patients received 100 mg of cortisol i.v. over a period of 10 min. Free fatty acids increased after 4 h, and cholesterol increased after 0.5 h. ACTH activates peripheral lipolysis, facilitating the hepatic synthesis of triglycerides. It exerts a stimulating action on the lecithin-cholesterol-acyl-transferase system. Cortisol acts by facilitating the synthesis of triglycerides in the liver and increasing the hydrolysis of triglycerides in the plasma.