The inhibitory effect of alpha-agonists noradrenaline and phenylephrine on the maximal alpha 1-adrenergic contractile response was studied in the rat isolated vas deferens and its epididymal and prostatic sections. The degree of noradrenaline (2.10(-5) M) inhibition of the maximal response was directly related to the magnitude of response to noradrenaline in the same concentration. The response of the epididymal section to phenylephrine reached its maximum and terminated faster than the response to noradrenaline. Both the activation and the desensitization seem to proceed faster in alpha 1-adrenoreceptors. The inhibition of the maximal response under the effect of phenylephrine (2.10(-5) M) was more obvious than the response to it in the same concentration. Noradrenaline seem to produce desensitization of alpha 1-adrenoreceptors involved in the response whereas phenylepinephrine produces desensitization in uninvolved ones, too.