The value of intraoperative blood flow measurement during clinical kidney grafting to predict subsequent function was studied in the course of 19 consecutive transplantations. The results indicate that when blood pressure and heart rate of the recipients are within normal limits there exists a significant relationship between renal blood supply and recovery of the kidney function. The operative blood flow into the graft correlated, moreover, with the state of presensitization of the recipients, as determined by antibody-against-panel assays. The possible causes of these relationships are discussed. It is emphasized that actual viability of allotransplanted kidneys depends on both pre-and intraoperative pathophysiological processes.