Marked increases in renal volume commonly occur in acute tubular necrosis and acute transplant rejection. Based on studies in the dog, we have previously suggested that the renal swelling observed in states of acute renal injury may be due principally to an increase in compliance of the kidney. The present study was undertaken in an effort to assess whether compliance-mediated increases in renal volume might affect renal function. In 15 dogs we compared the function of a decapsulated kidney (DK) to that of the contralateral intact kidney (IK); in 12 dogs we compared the function of a partially decapsulated kidney (PDK) to that of the contralateral IK. We compared the function of DK or PDK to IK, first under control conditions (ureteral pressure (UP) equals 0 mmHg), then at increased intrarenal pressure (UP equals 30 mmHg for both kidneys plus iv saline loading), and then during a recovery period (UP of both kidneys restored to 0 mmHg). The rationale is that probably DK is more compliant than IK; thus at increased intrarenal pressure DK volume should increase more than IK volume. Under control conditions DK and IK function were normal and equal; however, during increased intrarenal pressure, glomerular filtration rate (GFR) was about 20% less and Na and H20 excretion were about 30% less in DK than in IK. When intrarenal pressure was restored toward control by lowering UP to 0 mmHg, DK and IK function were once again equal. Similar but less marked changes occurred in the experiments comparing PDK and IK function. The impairment of renal function in DK vs. IK at increased intrarenal pressure was not explained by renal blood flow distribution, backdiffusion of glomerular filtrate, or by surface losses of fluid from DK. We suggest that impairment of renal function in DK vs. IK during increased intrarenal pressure is in some way related to the greater expansion of DK (21.0 +/- 0.02%) vs. IK (9.7 +/- 0.03%) at increased intrarenal pressure.