One hour incubation of slices prepared from rat liver or adrenal glands with 125I labeled lipoproteins of different classes resulted in label binding and its penetration into the tissue cells. The greatest amounts of labeling were found in fractions of mitochondria, lysosomes, microsomes and the final supernatant. In relation to the weight unit, slices from adrenal glands consumed several times as much label as did liver slices. Epinephrine increased the amount of the label bound to the low density lipoproteins by several times in the fractions of large cell membranes, and decreased the 125I level in mitochondria. Cortizole increased the incorporation of the protein labeled lipoproteins very low density into the liver mitochondria. ACTH did not influence the incorporation or cellular distribution of the label in adrenal glands.