The effects of carbamazepine administration into the nucleus tractus solitarii (NTS) on central alpha 2-adrenergic cardiovascular function were studied in normotensive Wistar Kyoto (WKY) and spontaneously hypertensive rats (SHR). Stereotaxic microinjections of carbamazepine (288 ng/60 nl) into the NTS of SHR transiently increased blood pressure, heart rate, and renal sympathetic nerve activity. These effects were followed by a modest depressor and bradycardic effect, with no change in sympathetic nerve activity. In addition, previous intra-NTS administration of carbamazepine attenuated the antihypertensive effect of the centrally acting alpha 2-adrenoceptor agonist, clonidine. Similar carbamazepine effects were observed in the WKY rats. These results suggest that some of the cardiovascular changes observed during carbamazepine treatment involve antagonism of central noradrenergic mechanisms.