Abstract The aim of the present experiment was that of studying the effect of an LHRH agonist analog on the prostatic content of cytosol and nuclear salt-extractable and salt-resistant androgen receptors (AR). Castrated rats were treated for six days with the LHRH agonist WY 40972 (A), with testosterone enanthate (T) or with A plus T. Intact adult male rats and castrated rats treated with the vehicle served as controls. The animals were sacrified 18 h after the last subcutaneous injection. The ventral prostates were quickly removed and submitted to subcellular fractionation for the determination of cytosol and nuclear AR content. In addition, the weights of the prostates and of the seminal vesicles were recorded, and serum levels of LH and FSH were evaluated by radioimmunassay. The dissociation constants (Kd) of cytosol and nuclear AR, on the order of 1×10 −9 M, were not affected by the various treatments. Conversely, the combined treatment with T and A induced a significant increase of nuclear AR in the prostatic tissue, when compared to the levels found in castrated rats treated with T alone and in intact rats. The treatment with T was able to restore the reproductive organs to their normal weights. The treatment with A inhibited the hypersecretion of gonadotropins induced by castration. The results show that, under the conditions of the present experiment, A exhibits a synergistic effect with T on nuclear AR content in the rat ventral prostate. The results also suggest that A acts directly on this androgen-dependent structure.