The substitution of glycine in position 6 by D-serine, and that of glycinamide in position 10 by ethylamide, leads to a nonapeptide with a greatly enhanced LHRH effect. The effects of buserelin on FSH and LH release are 20 to 170 times greater than those of LHRH. Buserelin acetate also has a longer duration of action than natural LHRH. Investigations in healthy adult males and females have demonstrated that the increase in plasma LH and FSH levels persist for at least 7 hours and that a return to basal values requires about 24 hours.Clinical inhibition of gonadotropin release, and subsequent reduction of serum testosterone or estradiol to castration level, was found when large pharmacologic doses (50-500 mcg SC/day or 300-1200 mcg IN/day) were administered for periods greater than 1 to 3 months. Chronic administration of such doses of buserelin results in sustained inhibition of gonadotropin production, suppression of ovarian and testicular steroidogenesis and, ultimately, reduced circulating levels of gonadotropin and gonadal steroids. These effects form the basis for buserelin use in patients with hormone-dependent metastatic carcinoma of the prostate gland as well as in patients with endometriosis.