Previous studies in this laboratory have demonstrated a delay in the elimination of lipids from the blood stream of hyperlipemic patients after intravenous fat infusion (1). These studies suggested a defect in the lipemia clearing mechanism in hyperlipemia. We subsequently found (2) that the serum of patients with hyperlipemia (primary and secondary to diabetes, nephrosis, glycogen storage disease) inhibited the heparin-induced lipemia clearing activity of normal serum. It was further found that the inhibitory activities of hyperlipemic serum were associated with the supernatant fatty layer obtained after highspeed centrifugation (3). Similar inhibitory activities as in hyperlipemic serum are present in human and other mammalian tissue (4). Since normal human and other mammalian tissue, like hyperlipemic serum, inhibit a number of lipase preparations as well as heparin-induced lipemia clearing activity (5, 6), they can be considered to have general antilipolytic action (7, 8, 9).