Leuprolide is the first member of the class of gonadotropin-releasing hormone (GnRH) agonist analog to be released in the U.S. The pharmacology of leuprolide is complex and not yet completely defined. This agonist analog is more potent than natural GnRH and appears to be capable of occupying pituitary GnRH receptors. This results in a "down regulation" of the receptors' activity and gonadotropin release, ultimately decreasing serum testosterone levels to those seen following castration. Leuprolide has been found effective in the palliative treatment of advanced cases of prostatic cancer and is not associated with the cardiovascular and thromboembolic toxicity seen with conventional diethylstilbestrol therapy. Leuprolide is administered by daily subcutaneous injections and has been generally well tolerated. The most common adverse effects are hot flashes and a possible flare-up of prostatic carcinoma symptoms on initial dosing. As clinical experience grows in the use of GnRH agonist analog, GnRH will assume a greater role in the treatment of metastatic prostatic cancer.