Mesterolone 25 is used to treat potency disturbances, infertility, and declining physical and mental M alertness in the aging male due to reduced androgen formation. It is an oral androgen which does not aromatize estrogen. It does not stimulate the body to produce testosterone but may act as an oral androgen substitute to compensate for a lack of the natural male androgen. It is suitable för treatment of all conditions caused by deficient endogenous androgen formation without impairment of spermato- genesis. It is effective as an anti-aromatase in the body, preventing or slowing the conversion of androgens into estrogens. Mesterolone 25 is well tolerated by the liver.