Experiments were performed in hydropenic, anesthetized dogs to investigate the effect of two dose levels of bumetanide on sodium excretion, urinary concentration, total renal blood flow and intracortical distribution of blood flow using the radioactive microsphere technique. Intravenous administration of bumetanide (0.025 mg/kg followed by 0.025 mg/min) did not alter blood flow within the kidney. A higher dose of bumetanide (0.1 mg/kg followed by 0.1 mg/min) significantly increased total renal blood flow and lowered renal vascular resistance. The rise in renal blood flow after bumetanide was due entirely to an increase in perfusion to the midcortical and juxtamedullary regions. A transient rise in plasma renin activity was measured only after the higher dose of bumetanide. Both doses of bumetanide increased sodium excretion and depressed solute free water reabsorption, although natriuresis was greater in response to the high dose. The results indicate that higher dose levels of bumetanide can increase total renal blood flow to the inner cortex. However, changes in renal blood flow were apparently not essential for the diuretic action of bumetanide because a significant natriuresis was observed in a setting where no change in intrarenal hemodynamics could be detected.