The effect of hypercholesterolaemia on the cholesterol and phospholipid content of spermatozoa and seminal plasma was studied. Testosterone and specific markers of the accessory sex glands were also measured. Semen samples from 11 hypercholesterolaemic patients (plasma cholesterol > 6.42 mmol/l, plasma triglycerides < 2 mmol/l) were compared with those of 11 normocholesterolaemic controls (plasma cholesterol < 5.14 mmol/l, plasma triglycerides < 2 mmol/l). Cholesterol, phospholipids and the molar ratio of cholesterol: phospholipids were not significantly different between the two groups of patients either in spermatozoa or in seminal plasma. In hypercholesterolaemic patients the total amount of carnitine in the ejaculate was significantly higher, but there were no significant differences in the levels of acid phosphatase or fructose. There were no significant differences in seminal plasma levels of testosterone in the two groups of subjects. These results suggest that hypercholesterolaemia has no effect on cholesterol and phospholipid levels in spermatozoa and does not cause gross modification of the secretory function of the accessory sex glands.