Extracellular recordings were made from neurones in the bed nuclei of the stria terminalis (BST) in brain slices from female rats on days 13-15 of pregnancy, during lactation or 5-6 days following weaning. The proportion of neurones excited by the oxytocin-specific agonist, Thr4, Gly7-oxytocin, did not change over the peri-partum period, but the magnitude of their response increased significantly during lactation. These data concur with reported changes in receptor density. It is suggested that increased oxytocin responsivity of BST neurones may subserve a regulatory function to maternal behaviour or neuroendocrine reflexes during lactation.