Renal toxicity resulting from injection of 12.5% NaCl and 25% urea solution in 0.9% NaCl was determined in blood and plasma perfused organs. The 25% urea solution was not toxic in either instance, however 12.5% NaCl in the blood perfused organ resulted in massive renal destruction and blood urea N elevations over 40 mg%. Plasma perfused kidneys injected with 12.5% NaCl revealed substantially less evidence of parenchymal damage and minor elevations of blood urea N levels. The results tend to support the hypothesis that red cell agglutination is involved in the toxic process in renal tissue resulting from exposure to hypertonic solutions.