SKF 64139, an inhibitor of phenylethanolamine-N-methyltransferase (PNMT), has a marked hypotensive effect in models of sodium-dependent hypertension. The mechanism of this effect is obscure, the compound having in addition alpha-adrenoceptor blocking properties. We compared the acute effects of SKF 64139 with those of LY 134046, another PNMT inhibitor with minimal alpha-blocking capacity, in desoxycorticosterone-salt hypertensive rats. The former agent produced profound hypotension whereas the latter caused only bradycardia. Both induced a similar pronounced suppression of PNMT activity in the C1 and C2 region of the medulla oblongata. These results suggest that the alpha-adrenergic effect rather than PNMT inhibition accounts for the acute lowering of blood pressure in this model.