An interdependence of the hormonal state of rodents and the genital muscle response to drugs was observed either on females or on males. Castration or castration followed by oestradiol treatment increased the responses of rat seminal vesicles to parasympathomimetic drugs. As, however, the influence of such procedures upon the responses to sympathomimetic drugs is controversial, the parameters pD2 (apparent affinity constant), alpha (intrinsic activity) and rho (relative responsiveness) of adrenaline, noradrenaline, methoxamine and phenylephrine on the seminal vesicles isolated from normal and castrated rats were determined. These parameters were shown to be different, depending not only of the hormonal state of the donor animals, but also of the drugs tested on each preparation. These facts must be considered in studies about sensitivity of rat seminal vesicles to sympathomimetic drugs.