Genistein, one of isoflavones, is structurally similar to mammalian endogenous oestrogens, which inhibit activity of tyrosine kinase, DNA topoisomerases, and possess antioxidant activity and oestrogenic activity. The aim of the present work was to study effects of the central administration of genistein on prolactin secretion in ewes during the seasonal anoestrus. The experiment was carried out on twelve Polish Lowland ewes. Infusions of genistein into the third ventricle of ewes were performed with calibrated 1.0-ml gas-tight syringes and a microinjection pump. Control infusions (n=4) from 12.01 to 16.01 h were done with a Ringer-Locke solution at flow rate 100 μl/h. The dose of genistein was 1 μg/100 μl/h (n = 6) and 10 μg/100 μl/h (n = 5) during 4-h infusions. Before the infusions, differences in prolactin concentration between control and experimental animals were insignificant. Prolactin concentrations were significantly (P<0.05) elevated after 2 h of genistein infusion (1 μg/h) as compared with the control group. The higher dose of genistein (10 μg/h) evoked an immediate increase of prolactin concentrations, which remained elevated (P<0.05) until the end of samples collection at 20.00 h. There was also significant (P<0.05) difference in prolactin concentrations, during the last 2 h of the blood collection, between ewes with different genistein doses. In conclusion, centrally administered genistein, stimulate the secretion of prolactin in dose-dependent manner in ewes during the seasonal anoestrus.