1. Ethacrynic acid reduces renal vascular resistance of the isolated dog kidney.
2. Ethacrynic acid induced natriuresis can occur despite stabilization of renal blood flow, but augmentation of blood flow increases the natriuretic response.
3. Vasodilatation and natriuresis after ethacrynic acid administration occurred together in time and were not separable. The onset and peak natriuretic and vasodilator responses frequently coincided in time.
4. Ethacrynic acid induced vasodilatation could be inhibited by loss of body fluid. The rise in resistance could be avoided by adequate volume replacement and by prevention of volume depletion.