The existence of small quantities of unesterified fatty acid in blood plasma has been known for some years. In particular, the finding of unesterified fatty acid (hereafter abbreviated UFA) in albumin fractions prepared from fresh human plasma by the methods of Cohn, Hughes, and Weare (1), and the report of Davis (2) clotting, and immediately chilled in ice water. Centrifugation was carried out in the cold, and the extract prepared within four hours. These precautions were intended to reduce in vitro lipolytic action which might cause artifactual elevation of the UFA concentration.Cold storage of normal or lipemic plasma samples for periods of up to four hours has been shown not to result in significant changes of UFA concentrations. To 2 ml. of plasma were added, in order, 1 ml. phosphate buffer of pH 6.0 and molarity 0.2, 1 ml. 5 per cent sodium dodecyl sulfate, 9 ml. saturated aqueous sodium sulfate, and finally a slight excess of anhydrous sodium sulfate powder. The reagents utilized were of the best commercial grade. Five extractions with 2-ml. portions of ethyl ether were carried out as described by Davis. After gentle evaporation of the ether, the residue was taken up in 5 ml. 95 per cent alcohol, a drop of approximately .01 normal sulfuric acid was added, and the solution titrated. The titrant was .02 normal sodium hydroxide (aqueous solution) delivered from a Gilmont ultramicroburette. CO-free air served to stir the solution, and the titration was followed with a Beckman Model G glass electrode pH meter. Titration between the apparent

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The clinical syndrome of idiopathic hyperlipemia is, characterized by lactescent blood plasma in the postabsorptive state. The milky appearance of the plasma is caused by its abnormally high content of triglyceride-rich lipoproteins of high molecular weight. Omission of fat from the diet of such patients decreases the concentration of triglycerides, suggesting that defective removal of exogenous fat from the circulation may be an important metabolic abnormality in this syndrome.The heparin-activated enzyme, lipoprotein lipase, is thought to be concerned with removal of newly absorbed fat from the blood. The basis for this assumption rests on the accelerated removal of chylomicrons from the blood after injection of heparin, which liberates the enzyme into the circulation, resulting in lipolysis in the blood plasma itself (1); the retarded removal of chylomicrons from the blood after administration of antiheparin agents such as protamine sulfate (2); the preferential hydrolysis by the enzyme of triglycerides associated with lipoproteins (3); and the rapid conversion of the fatty acids of intravenously injected chylomicrons into circulating free fatty acids (4).A deficiency of lipoprotein lipase would be expected to result in excessive and prolonged chylomicronemia after ingestion of fat, and thus might be a basic cause of idiopathic hyperlipemia.We undertook the present investigation to examine this hypothesis and to study lipid transport in the blood of three hyperlipemic siblings of a family of eight, who were previously described by Gaskins, Scott and Kessler (5). The results suggest that a deficiency of lipoprotein lipase is * Portions of this work were presented to the American Society for the Study of