The authors presented the results of a study of hormonal function of the hypophy-seogonadal system in papyo hamadryad males subjected to continuous infusion of buzereline (LH-RH agonist) at a daily dose of 3 μg/kg of body mass for 4-6 weeks with the help of subcutaneously implanted osmotic mini-pumps. A two-phasic response of the system to the drug was established. Activation of the secretion of hypophyseal gonadotrophins and testicular androgens in the first days of buzereline infusion was followed by sharp inhibition of endocrine function of the hypophyseogonadal system. Functional tests with the administration of LH-RH (100 μg) and human chorionic gonadotrophin (1500 U) to experimental animals demonstrated the leading role of the development of adenohypophyseal desensitization in the mechanism of antifertile drug action.