An ivestigation was made of the effect of the duration of posttransplant renal failure on the late prognosis of graft as well as patient survival and on the frequency of complications in 102 patients who had a functioning graft at three months after transplantation. A direct correlation was found between duration of acute tubular necrosis (ATN) and the late prognosis of the graft. The creatinine clearance was significantly higher and the frequency of complications was lower in the group with immediate resumption of renal function. The mortality rate increased with the duration of ATN.