A semi-automated blood perfusion apparatus is presented as a tool for the in vitro assessment of renal function. Kidneys are blood perfused under computer-controlled conditions. The blood perfusate is oxygenated and circulated in a closed system through the cannulated renal vein and artery using a pulsatile blood pump. Urine output is determined using a drop counter, and the urine is then analyzed but not recirculated. The volume of circulating fluid is constantly adjusted. Blood gas sensors placed on the arterial and venous lines to permit on-line monitoring, and the data are used to calculate oxygen consumption. Blood and urine specimens are collected in timed intervals and are used to calculate the standard renal function parameters. The function parameters of seven control blood perfused kidneys are consistent with those found in the literature. Thus, this system represents a practical approach to the in vitro semi-automated testing of kidneys.