Mammary lactogenic response was obtained in the male rat following a single injection of reserpine (1mg/kg). The lactogenic effect of reserpine was rather long-lasting and the response of the mammaryglands was biphasic. As previously reported (Arai and Suzuki, 1971), the initial peak of the lactogenic response was recognized on day 2, the second one around day 8. Administration of ergocornine (1mg/rat) concurrently with reserpine inhibited the initial phase of lactogenic response when autopsied on day 2. The secondary lactogenic response was also inhibited when ergocornine wasgiven on day 4 or day 6 and autopsied on day 8, but not inhibited when ergocornine wasgiven concurrently with reserpine and autopsied on day 8. These results suggest that ergocornine acts at a different level from that of the lactogenic action of reserpine to prevent pituitary prolactin release, and also suggest that alterations in the hypothalamus caused by reserpine may be primarily responsible for the biphasic release of pituitary prolactin in the male rat.