Evidence from previous theoretical and experimental studies has indicated that angiotensin formed as a result of unilateral kidney disease will not produce chronic hypertension unless there is also a sodium and fluid retaining effect on the otherwise normal contralateral kidney. Therefore, the present experiments were conducted in dogs to determine whether or not blood angiotensin concentrations similar to those found in patients with unilateral kidney disease can cause significant water and salt retention by a normal dog kidney. Angiotensin was perfused directly into the renal artery of a semi-isolated perfused kidney preparation, and the effects on renal blood flow, glomerular filtration rate, degree of autoregulation of both renal blood flow and glomerular filtration rate, and rates of excretion of electrolytes and water were all determined at perfusion pressures between 75 and 200 mm Hg. The results showed that angiotensin in reasonably low dosages can cause the normal dog kidney to retain water and salt, but from a quantitative point of view it remains doubtful whether or not enough angiotensin is formed in patients with unilateral kidney disease to produce a similar effect. Studies on the various parameters of kidney function gave an insight into the mechanism of water and salt retention during angiotensin infusion and also explained why angiotensin infusion sometimes causes diuresis rather than antidiuresis.