SUMMARY Both oestradiol and perphenazine induced a significant increase in prolactin release by ovariectomized rats. Ergocornine completely inhibited the initial perphenazine-induced prolactin release which normally reaches a maximum during the first 2·5 h. However, ergocornine did not prevent a significant increase in prolactin release after daily administration of perphenazine. It inhibited oestrogen-induced prolactin release. The results support earlier suggestions that prolactin release is controlled by two mechanisms. Only one of the mechanisms can be blocked by ergocornine.