The effects of human native and Cuz+-oxidized low-density lipoprotein (LDL) were tested on the migration of cultured bovine aortic smooth muscle cells (SMCs) in blind-well chambers. LDL oxidation was controlled by measuring the formation of conjugated dienes and lipid hydroperoxides, and by agarose gel electrophoresis. Oxidized LDL stimulated SMC migration, and the effect was dose-dependent up to 200 ,ug/ml. The stimulation was chemotactic in nature. Native LDL was without significant activity. The results suggest that oxidized LDL may contribute to the migration of medial SMCs into the intima during atherogenesis.