The relative rates of hepatic 3H incorporation into digitonin-precipitable sterols (DPS) and release of labeled D PS into the plasma were compared between copper-deficient (CUD) and copper-adequate (CuA ) rats. Following intravenous injection of 3H20 and Triton WR 1339, the liver and plasma 3H-DPS radioactivities were measured at 2, 4, 6, and 8 hr, and the net total accumulation of plasma cholesterol (CH) and triglyceride (TG) was determined during the 8-hr period. In both groups, the liver synthesis of 3H-DPS displayed a biphasic curve, with an initial slow rate up to 4 hr, followed by a rapid increase starting at 6 hr. During the latter phase, a notable increase in liver 3H-DPS radioactivity was observed in CuD rats, but the plasma release of 3H-DPS did not significantly change, despite the increased synthesis of 3H-DPS in the liver. In both groups, the net total accumulation of CH in the plasma, as expressed in mmol CH/IO0 g body weight, increased steadily from 1.2 mmol at 2 hr to 4.7 mmol at 8 hr, while plasma TG accumulated at a much greater rate ranging from 3.3 mmol at 2 hr to 13.6 mmol at 8 hr. There was no significant difference in net total accumulation of CH or TG in the plasma between the groups at any given interval. The results provide evidence that copper deficiency stimulates the liver synthesis of cholesterol, but that it does not result in an accelerated release of newly synthesized cholesterol from the liver involving very low density lipoproteins (VLDL). Thus, the present findings suggest that the hypercholesterolemia induced in copper deficiency is not attributable to a stimulation of the hepatic release of VLDL cholesterol into the plasma.