Anabolic steroids have widespread metabolic effects but, to date, their proven clinical indications have been limited. Recently the 17 alpha-alkylated steroid, stanozolol, has been shown to be of value in a variety of commonly occurring vascular diseases. Its endocrine effects have received little attention and we have investigated the effect of administering a 14 d course of stanozolol (10 mg orally per day) on a variety of important hormonal pathways in nine healthy male subjects. Significant changes occurred as follows: a 55% reduction in serum testosterone levels was noted and was accompanied by reductions in 'derived' free testosterone, sex hormone binding globulin and LH levels; total T4 and T3 levels fell in association with a decrease in thyroxine binding globulin, but no alteration was detected in TSH or free T4 levels. Changes in vitamin D status, with falls in 25-hydroxycholecalciferol and vitamin D binding globulin were also observed. These effects were reversible on stopping treatment. Stanozolol therapy therefore leads to a number of hormonal changes, probably by an action at both pituitary and hepatic levels.