Because testosterone is rapidly metabolized by the liver, it is necessary either to administer androgens by injection in the form of testosterone esters that are absorbed slowly into the circulation or to administer by mouth derivatives that are slowly metabolized by the liver. The later derivatives, however, have deleterious side effects that limit their usefulness. Long-acting parenteral androgen esters are the treatment of choice in the replacement therapy of male hypogonadism. Because these esters must be hydrolyzed to the free hormone prior to exerting their cellular actions the effectiveness of therapy can be monitored by following plasma testosterone levels. All known effects of the endogenous hormone can be duplicated except for the induction and maintenance of normal spermatogenesis. Androgens have been tried in a variety of clinical situations other than male hypogonadism in the hopes that the nonvirilizing actions would outweigh any detectable side effects. The only disorders in which a salutary effect has been documented are hereditary angioneurotic edema and some patients with anemia due to failure off the bone marrow.