Changes in functional properties and hemodynamics of isolated kidneys were analysed with special regard to pressure and duration of perfusion. Observations were compared between pairs of kidneys taken from the same animal and placed in identical experimental situations, but respectively perfused at a pressure level of either 100 mm Hg or 160 mm Hg. 2. A method using 133Xenon wash-out to measure renal blood flow, suppressing early recirculation, is described. 3. Changes in functional properties were towards decreases of glomerular filtration and tubular transfer. Hemodynamic changes proceeded from decreases of total and regional renal vascular resistance. Both functional properties and hemodynamic changes were larger as the duration of the pressure of the perfusion became greater. 4. Renal blood flow was different when measured with an electromagnetic flowmeter and by the 133Xenon wash-out technique. Practical applications, theoretical basis and results of the latter method are criticized. 5. Possible mechanisms by which high perfusion pressure hastens and increases functional and hemodynamic changes of isolated kidneys are discussed.
