Before and after androgen replacement therapy prostatic and seminovesicular volume was estimated by means of transrectal ultrasonography in 13 hypogonadal men. Volume of the prostate (p less than 0.001) and seminal vesicles (p less than 0.01) significantly increased after treatment with testosterone enanthate. However, the plasma level of testosterone remained abnormally low. These results indicate that volume determination of the prostate and seminal vesicles by means of transrectal ultrasonography is suitable for evaluating the adequacy of androgen replacement therapy in male hypogonadism.