SummarySome of the peripheral actions of clonidine have been investigated in nonnal volunteers. Close intra‐nrterial administration of clonidine (125–500 μg./min.) into the brachial artery caused a rapid constriction of the skin vessels in the foreann and the hand. The response was dose‐dependent and did not show tachyphylaxis during a thirty minute infusion. It was absent in the presence nl adrenerjjic alpha receptor blockade, which indicates a sympathometic mode of action. Reflex vascular sympathetic responses were still elicited during the intra‐arterial infusion, therefore neuronal or alpha receptor block was not present at the doses of clonidine used.Intravenous infusion of 150 μg. clonidine caused a 16% fall in mean arterial pressure, a biphasic change in calculated hand vascular resistance and a fall in heart rate. The patteni of vascular resistance changes reflects a direct vasocon‐ strictor action of the drug which is then overshadowed by its central sympathetic inhibitory action. The vasoconstrictor response to intra‐arterial nonitlrenaline was greater during the hypotension produced by clonidine. Similarly, tbe pressor response to intravenous noradrenaline was accentuated at this time. At least with acute administration of clonidine to man, reduced vascular responsiveness cannot play any part in the hypotension which occurs.