The theory of renal counterbalance was introduced by Hinman1 in 1922. Before this article appeared, little, if anything, had been written concerning the possibility of renal atrophy of disuse, and according to Hinman this type of renal atrophy was a new conception, even though a similar process had long been recognized in other organs, such as muscle and bone. It is remarkable that a conclusion had not been crystallized concerning atrophy of disuse when applied to the kidney. Indeed, the subject seems to have been unnoticed until Hinman applied it as the basis for his theory of renal counterbalance. According to this theory, a kidney, after sustaining a temporary injury, as, for example, a temporary period of ureteral obstruction causing hydronephrosis, will go on to complete or almost complete atrophy if allowed to function in competition with its hypertrophic mate. Thus, if the ureter of a kidney is obstructed