Development of noradrenergic responses in the rat dorsal motor nucleus of the vagus (DMV) from postnatal days 0 to 22 was studied by a conventional microelectrode technique using brain slice preparations. Between postnatal days 0 and 6, noradrenaline (NA) caused only alpha 1-adrenoceptor-mediated depolarizations. By postnatal day 14, alpha 2-adrenoceptor-mediated hyperpolarization appeared. During the next postnatal week, the response pattern to NA became similar to that in adults, including both alpha 1- and alpha 2-adrenergic responses. These results suggest that alpha 2-adrenergic responses in DMV neurons are absent at birth but develop rapidly in the 3 weeks after birth. Furthermore, alpha 1-adrenoceptors have already been functioning in the fetal period.