Blood flow in the portal vein and in the hepatic artery measured with ultrasonic transit time flowmetry during septic shock. A continuous infusion of vasopressin (0.06 IU/kg per hour) was started at t = 300 minutes in animals in group SV. Animals in group S received intravenous saline only. Results are presented as individual curves. Portal venous and hepatic arterial blood flows are indexed to body weight. There was a significantly greater decrease in portal venous blood flow in group SV than in group S (p < 0.01). Hepatic artery blood flow remained virtually unchanged in all animals in group S and in five out of eight in group SV. Three animals in group SV may have had some hepatic arterial buffer response. #p < 0.01 compared with t = 300 minutes. Group S, septic control group; group SV, septic test group treated with vasopressin.