The goals of hormonal treatment of male hypogonadism depend upon the stage of sexual development in which gonadal failure occurs. Androgen replacement therapy is used to induce and maintain normal secondary sexual characteristics, sexual function, and behavior in prepubertal boys and men with either primary or secondary hypogonadism. Parenteral testosterone esters, testosterone enanthate or cypionate, are the most effective, safe, practical, and inexpensive androgen preparations available for this purpose. They are the treatment of choice for androgen replacement therapy. A recently approved scrotal transdermal testosterone system provides an alternative to testosterone esters in selected patients. In boys or men with secondary hypogonadism, gonadotropin or GnRH therapy may be used instead of testosterone therapy to stimulate endogenous testosterone production. Because of their greater expense and complexity, however, these modalities are usually reserved for men with gonadotropin deficiency who desire fertility and in whom spermatogenesis must be initiated and maintained. Gonadotropin therapy is begun with hCG alone. In men with partial or previously treated gonadotropin deficiency, or in men with postpubertal hypogonadotropic hypogonadism, hCG treatment alone may be sufficient to stimulate spermatogenesis and fertility. In most men with prepubertal hypogonadotropic hypogonadism, however, combined treatment with hCG plus hMG is needed to initiate sperm production and fertility. Pulsatile GnRH therapy may be used to stimulate testosterone production and spermatogenesis in men with secondary hypogonadism who have hypothalamic defects, such as idiopathic hypogonadotropic hypogonadism or Kallmann's syndrome.