1. To assess whether diazoxide-induced sodium retention is due to a direct renal action of the drug, independent of its systemic haemodynamic effects, diazoxide was infused directly into one renal artery of hydropenic rats. During the infusion period there was a small fall in mean systemic arterial blood pressure. There were no significant changes in the clearances of inulin or p-aminohippurate by either kidney.
2. Absolute and fractional excretion of sodium were unchanged on the non-infused side. On the side of infusion, there was a significant increase in absolute and in fractional sodium excretion.
3. Thus natriuresis rather than sodium retention seems to be the direct renal effect of diazoxide and may be related to its vasodilator properties.