IN 1940, one of us and M. Dor investigated in the dog the relationship between renal blood flow, systemic pressure and oxygen consumption in kidneys transplanted in the neck. We found that between 60 and 150 mm. Hg. increase in the blood pressure raised the renal blood flow, but that from about 100 mm. up to 160 mm. there was no relationship between blood pressure and blood flow in the kidney. We concluded that "Pour les reins enerves, les valeurs critiques de pression et de debit veineux sont de l'ordre de 130 mm. et 3 c.c. respectivement. Au-dessus de ces chiffres, debit veineux et consommation d'oxygene varient beaucoup plus en fonction d'autres facteurs encore inconnus qu'en fonction du regime de la pression ou de la circulation".Later [Brull and Louis-Bar, 1950], using a mechanical heart with coagulable blood [Brull, 1950], we extended our investigation to include pressures up to the limit of resistance of the renal capsule. The urine flow followed regularly the variations in arterial pressure. The venous flow, although eventually influenced by variations of arterial pressure, did not follow so closely in 7 cases out of 16; it did not respond at all in 9 cases out of 16. We suggested that it was necessary to find out whether the blood carries to the kidney one or several factors which regulate vasomotor responses as well as secretion.In the meantime, Selkurt, Hall and Spencer [1945] investigated, by indirect measurement of the blood flow, the problem which we had studied in 1940. Although unaware of our results, they came to the: same conclusions. In 1951, Shipley and Study perfused kidneys at low, normal and high pressures, using a Dale-Schuster pump and heparinised blood. Unaware of our results of 1950, they too arrived at similar findings, but emphasised that at very high pressures the blood flow, hitherto independent of the pressure, was again influenced. Recently, Brull and Louis-Bar [1953] perfused innervated kidneys in situ, using a mechanical heart with coagulable blood, and showed that innervated kidneys were even more independent of the systemic pressure than denervated ones. Our results were similar to those of Shipley and Studv.151