Starting from experimental observations demonstrating that a high ratio of zinc to copper led to hypercholesterolemia in rats, serum Zn and Cu levels were measured by atomic absorption spectrophotometry in 65 normolipemic controls and in 100 subjects with various types of hyperlipoproteinemia (HLP). Serum Zn levels did not significantly differ from control values in any type of HLP. However, hyperlipoproteinemic patients with obvious clinical atherosclerosis displayed significantly lower serum-Zn concentration than hyperlipo-proteinemic subjects without clinical symptoms. On the other hand, when compared to control subjects, serum Cu levels were not found to be decreased, but rather increased, in hyperlipoproteinemic patients with or without atherosclerosis. As a result, the Zn∶Cu ratio appeared to be lower than normal in hyperlipoproteinemic patients with cardiovascular disease. It is conceivable that changes of these trace elements should be rather connected to vessel injury and associated disease than to HLP which, at least in humans, is not accompanied by a high Zn∶Cu ratio.