I Intraventricular a-methyldopamine (50-200 gg) produced a dose-related fall in blood pressure in conscious spontaneously hypertensive rats. Pretreatment with intraventricular 6-hydroxydopamine prevented this hypotensive effect of a-methyldopamine. 2 The hypotensive effect of a-methyldopamine was prevented by intraventricular injection of phentolamine or desmethylimipramine, but not by intraperitoneal injection of haloperidol.3 Pretreatment with U-14,624, a selective central dopamine-4-hydroxylase inhibitor, prevented the hypotensive effect of a-methyldopamine. 4 cx-Methyldopamine was considerably less potent than noradrenaline as a pressor agent in the pithed rat, but noradrenaline and cx-methylnoradrenaline were found to be equipotent. 5 a-Methyldopamine (1-5 mg i.c.v.) reduced pressor responses elicited by electrical stimulation of the midbrain reticular formation in cats anaesthetized with chloralose. 6 It is concluded that the hypotensive action of ca-methyldopamine in conscious animals involves intact central ca-adrenergic neurones and a central adrenergic uptake mechanism for the formation of a-methylnoradrenaline.