A study was made of the effects of a single injection of anterior pituitary purified growth hormone (GH) on lipid distribution and phospholipid turnover in plasma, liver and aorta a few hours after administration in intact rabbit. Plasma glucose and liver glycogen concentration, and total liver weight were moderately, but significantly, increased after growth hormone. Contents of all lipid fractions of plasma and entire liver were significantly increased after GH while the only change in the aorta lipids was a significantly decreased neutral fat. Liver total lipid content was increased 64%, plasma total lipid increased 85%, and aorta total lipid was decreased 25%. The relative contribution of each lipid fraction to percentage increased or decreased total lipid determined in these tissues was: in liver, neutral fat contributed 47%, phospholipid 15%, and free and ester cholesterol 1.5% each; in plasma, neutral fat contributed 53%, PLP 19%, free cholesterol 6%, and esterified cholesterol 8%; in the aorta, neutral fat contributed 100% to the total change. Radioactivity data showed an accelerated synthesis of liver and plasma phospholipids occurred after GH treatment, but no such effect found upon aortic phospholipids. It is suggested that increased rate of formation of liver and plasma phospholipids need not necessarily be a specific effect of GH but a change in this parameter of metabolism subsidiary to enhanced mobilization of endogenous fat due to GH. It is further suggested that all elements of altered distribution of lipids in tissues analyzed could be explained in accordance with the concept of a primary adipo-kinetic action of growth hormone. The possible relationship of GH to the altered state of lipid metabolism in atherosclerosis is discussed.