Intracellular recordings were obtained from vagal neurones and their response to oxytocin was investigated in slices from the rat brainstem. Following recording, Lucifer Yellow was injected into the cells in order to verify their localization within the dorsal motor nucleus of the vagus nerve. Virtually all neurones throughout the rostro-caudal extent of the nucleus increased their rate of firing in the presence of 10-1000 nM oxytocin and their membrane depolarized in a reversible, concentration-dependent manner. This excitation was probably exerted directly on the impaled cells rather than being synaptically mediated, since it persisted in a low calcium-high magnesium medium or in the presence of tetrodotoxin. These data provide evidence for a direct membrane effect of oxytocin on a defined population of neurones in the rat brain.