We studied the hemodynamics in four groups of rats with combinations of mesenteric hypertension and portal diversion. Operations created three groups with mesenteric hypertension and different degrees of portal venous diversion: mesenteric vein stenosis, portal vein stenosis and end-to-side portacaval anastomosis with mesenteric vein stenosis, the fourth group had only portacaval anastomosis. A control group had sham operations. Cardiac output, splanchnic blood flows and portosystemic shunt indices were measured with radioactive microspheres. Mesenteric venous pressures in the mesenteric-stenosed, portal-stenosed, portacaval-shunted and end-to-side portacaval anastomosis with mesenteric vein stenosis rats were, respectively, 13.5 ± 0.6, 15.3 ± 0.7, 4.3 ± 0.5 and 13.0 ± 0.9 mm Hg, which were all significantly different from controls: 8.3 ± 0.3 mm Hg. Portosystemic shunt indices were also significantly different from each other: controls, 0.4% ± 0.02%; mesenteric-stenosed, 5.9% ± 2.3%; and portal-stenosed, 52.1% ± 4.9%. Cardiac output and splanchnic visceral blood flows were significantly increased in the portal-stenosed rats and the two groups with portacaval anastomoses, with the latter two groups having the highest values. The addition of mesenteric stenosis did not change the blood flows because mesenteric-stenosed rats did not differ from controls and end-to-side portacaval anastomosis with mesenteric vein stenosis rats did not differ from rats with portacaval anastomosis alone. These results suggest that mesenteric venous hypertension per se does not affect hemodynamics but that diversion of portal venous blood from the liver is a critical factor in the development of hyperkinetic circulation in portal hypertension. (HEPATOLOGY 1992;15:117–121).