It has been suggested that low serum cholesterol interferes with brain serotonergic functioning, which results in increased suicidal and aggressive tendencies. To test this hypothesis we investigated the relationship between serum cholesterol, high-density lipoprotein (HDL), low-density lipoprotein (LDL) and triglyceride levels, and serotonin uptake by blood platelets in 17 healthy men aged 39.5 +/- 10.2 years. Platelet serotonin uptake and serum lipids were assayed concomitantly for each individual. Serum cholesterol levels and other serum lipid levels did not correlate with serotonin uptake by platelets at the concentration of 2 x 10(-5) M (a concentration within the maximal uptake capacity range). The results indicate no influence of cholesterol on serotonin uptake, as opposed to some investigators who suggested that high risk of suicide and aggressiveness in hypocholesterolemic individuals is related to impaired serotonin transport.