We examined the extent to which supraphysiological doses of androgen can modify body composition and strength in normally virilized men. In doubly blind tests, 30 healthy young men received testosterone enanthate (TE) or 19-nortestosterone decanoate (ND), at 100 mg/wk or 300 mg/wk for 6 weeks. The TE-100 mg/wk group served as replacement dose comparison, maintaining pretreatment serum testosterone levels, while keeping all subjects blinded to treatment, particularly through reduction in testicular volumes. Isokinetic strength measurements were made for the biceps brachii and quadriceps femoris muscle groups before treatment and 2-3 days after the 6th injection. Small improvements were noted in all groups but the changes were highly variable; a trend to greater and more consistent strength gain occurred in the TE-300 mg/wk group. There was no change in weight for TE-100 mg/wk but an average gain of 3 kg in each of the other groups. No changes in 4 skinfold thicknesses or in estimated percent body fat were observed. Of 15 circumferences, significant increases were observed only for men receiving TE-300 mg/wk (shoulders) and ND-300 mg/wk (shoulders and chest). The data suggest that high dose androgens increase body mass and may increase strength in normal men but, except for a consistent weight gain with greater than replacement doses, the detectable changes were highly variable and relatively small, especially in comparison to the significant alterations which were observed for other markers of androgen action.