Diazoxide has potent inhibitory effects upon vascular smooth muscle tone, insulin secretion, natriuresis, and uric acid excretion, suggesting that its receptor site is a biochemical pathway common to the maintenance of each of these processes. Following reports of dependence of hypotensive activity upon the rate of intravenous injection, it has been postulated that arteriolar diazoxide receptor sites possess unique properties in that they must be filled rapidly to produce sustained arteriolar dilatation. Three milligrams of diazoxide per kilogram body weight was administered intravenously over 30 minutes and subsequently over 30 seconds to ten hypertensives. Sustained blood pressure reduction, hyperglycemia, reduction of plasma insulin levels, and reductions of urinary water, electrolyte, and uric acid excretion were induced by this dose of diazoxide. However, no significant difference in any of these effects was demonstrable between phases of rapid and slow injection. For all important effects of diazoxide, the response appears dependent upon equilibrium of receptor sites with circulating drug concentration, and no special properties of these sites need be postulated.