The effects of bunazosin, an alpha 1-adrenergic receptor antagonist, on low-density lipoprotein (LDL) receptor activity have been studied in cultured cells. Human skin fibroblasts, swine aortic smooth muscle cells and a human hepatoma cell line (Hep G2) were used for this study. Bunazosinm, at a concentration of 5 x 10(-5) to 10(-4) M, increased 125I-LDL uptake with all of the cell lines and 125I-LDL degradation with human skin fibroblasts and swine aortic smooth muscle cells. However, in human skin fibroblasts pretreated with lipoprotein deficient serum and Hep G2 cells, the degradation of 125I-LDL was decreased by bunazosin. These results suggest that bunazosin increases LDL receptor activity.