Marked increases in renal volume commonly occur in states of acute renal injury such as acute tubular necrosis or transplant rejection. This expansion appears to be due to a marked increase in compliance of the kidney. The present study examined whether compliance-mediated expansion of renal volume above normal impairs renal function. In each of 11 dogs, we compared the volume and function of a collagenase-treated kidney (CK) to the contralateral intact kidney (IK), first under control conditions, then when both kidneys were subjected to the same conditions to increase intrarenal pressure (raised ureteral or renal venous pressure) and then on return of intrarenal pressure toward control levels. The rationale is that since CK compliance exceeds IK compliance, the absolute difference between CK and IK volume is maximized at increased intrarenal pressure but minimized at normal intrarenal pressure. We found that CK and IK function were equal at normal intrarenal pressure. However, at increased intrarenal pressure there was suppression of GFR and sodium and water excretion in CK vs. IK. On return to normal intrarenal pressure, CK and IK function were, once again, equal. We also found that the difference in CK vs. IK volume correlated with the differences in CK vs. IK function. Thus, acute expansion of renal volume above normal impairs renal function.