During the last fifty years many investigators have turned their attention to the study of the effect of increased intra-ureteral pressure on the kidney parenchyma. Much of the work has been carried on in an effort to ascertain the effect of ureteral ligation, with the result that the pathologic processes involved were found to follow a definite sequence. Then again, the relation of these pathologic lesions to renal function has been studied in various ways, usually on a single kidney with the opposite organ intact. With the introduction of newer methods for the study of renal function, particularly in the last fifteen years, we have thought it of interest to investigate the conditions brought about by subjecting a kidney to back pressure while it was still eliminating the waste products of metabolism. By partially obstructing one ureter with a small rubber band and removing the opposite kidney, Keith and Snowden