Partially purified platelet-derived growth factor stimulates low density lipoprotein binding and degradation in cultured aortic smooth muscle cells of monkeys by increasing the number of available low density lipoprotein receptors. When platelet-derived growth factor was added to quiescent cells, low density lipoprotein binding increased within 4-8 hr. Stimulation of low density lipoprotein receptor activity preceded stimulation of DNA synthesis by platelet-derived growth factor by 8-12 hr. Enhancement of endogenous cholesterol synthesis by platelet-derived growth factor preceded stimulation of low density lipoprotein receptor activity. These findings suggest that the platelet-derived growth factor can increase both the exogenous and endogenous supplies of cholesterol to the cell for its use during cell proliferation.