Cholesterol and cholesterol esters were measured on day 90 in the plasma and aortas of rats treated on day 4 as follows: control, gonadectomy, testosterone propionate (TP), estradiol-17 β (E). Sex differences were observed in sterol concentrations of control animals but were abolished by castration. TP and E significantly altered sex gland weights, aorta cholesterol and plasma cholesterol esters of both sexes. Little effect on plasma cholesterol or esterified cholesterol of the aorta was noted in any treatment group. A dose effect of E was observed in organ weights and sterols of male rats.