The effect of increased intra-abdominal pressure on cardiac output and renal function was investigated using anesthetized dogs into whom inflatable intraperitoneal bags were placed. Hemodynamic and renal function measurements were made at intra-abdominal pressures of 0, 20, and 40 mmHg. Renal blood flo and glomerular filtration rate decreased to les than 25% of normal when the intra-abdominal pressure was elevated to 20 mmHg. At 40 mmHg intra-abdominal pressure, three dogs became anuric, and the renal blood flow and glomerular filtration rate of the remaining dogs was 7% of normal, while cardiac output was reduced to 37% of normal. Expansion of the blood volume using Dextran-40 easily corrected the deficit in cardiac output, but renal blood flow and glomerular filtration rate remained less than 25% of normal. Renal vascular resistance increased 555% when the intra-abdominal pressure was elevated from 0 to 20 mmHg, an increase fifteen-fold that of systemic vascular resistance. This suggests that the impairment in renal function produced by increased intra-abdominal pressure is a local phenomenon caused by direct renal compression and is not related to cardiac output.