This study describes the use of a blood perfusion apparatus to assess the renal function of isolated kidneys. Eight fresh kidneys were obtained from healthy rabbits and perfused with blood at 36°C for 2 hours. Rabbit blood was drawn and diluted to a hematocrit of 25%. The kidneys were evaluated for their capacity to support life in an autograft model. Blood and urine samples were taken at regular time intervals during kidney perfusion. Serum creatinine was measured in surviving rabbits after transplantation. Over the course of the perfusion, arterial pressure was maintained at 87.2 ± 5.5 mm Hg. The renal blood flow (3.7 ± 1.0 ml/min per g) and urine output (0.11 ± 0.04 ml/min per g) were continuously monitored. Glomerular filtration rate (0.29 ± 0.02 ml/min per g) and fractional reabsorption (FR) of sodium and glucose indicated appreciable tubular function (FR(Na) = 67.9 ± 8.5%, FR(Glu) = 91.2 ± 5.8%). Protein was excluded from urine at 99.8% ± 0.1%. After transplantation, the peak creatinine was 6.8 ± 3.2 mg/dl at 1.90 ± 0.92 days for the seven surviving rabbits and was above 16 mg/dl for the only rabbit that died 4 days after operation. The level of free hemoglobin generated at the end of the perfusion (2.6% ± 2.8%) was correlated with the postoperative peak creatinine (r2 = 0.84). Perfusion of seven additional kidneys by using the roller pump lead to a final hemolysis of only 0.34 ± 0.14%. Kidneys transplanted after 2 hours of blood perfusion were able to resume normal function and support life. Hemolysis was a measurable stress factor causing delayed function of the kidney after transplantation. Introduction of a roller pump significantly reduced the hemolysis.