Summary 1. Hepatic blood flow has been correlated with the metabolic and pathologic results of either side to side or end to side portacaval shunts or portacaval transposition in both normal and cirrhotic dogs. 2. The estimated hepatic blood flow (EHBF) was obtained by measurement of the rate of disappearance from arterial blood of radioactively labeled colloidal gold particles. In normal dogs, the mean EHBF was 46.4 cc./kg. body weight per minute. In dogs with end to side or side to side portacaval shunts EHBF averaged 27.5 cc./kg./min. and 19.6 cc./kg./min., respectively, in contrast to dogs with portacaval transposition in which the EHBF remained normal at 43.6 cc./kg./min. 3. In the dogs with either type of shunt, when the hepatic blood flow was reduced, blood ammonia rose, serum albumin fell, BSP clearance fell moderately and the packed cell volume decreased slightly. No metabolic abnormalities developed in dogs with portacaval transposition. 4. The preoperative EHBF in cirrhotic dogs averaged 42.8 kg. per minute. After portacaval transposition, EHBF remained virtually unchanged (39.2) but fell to 18.9 or 17.9 in cirrhotic dogs subjected to side to side or to end to side portacaval shunts. 5. The fall in concentration of serum albumin and rise in globulins that were characteristic of the cirrhotic animals continued or became more pronounced after either type of portacaval shunt. A significant rise in blood ammonia occurred in both groups of shunted animals. Cirrhotic dogs with portacaval transposition, in contrast, exhibited no further decline in hepatic function as compared to their own preoperative state. 6. Portal venous pressures, which were uniformly elevated in all cirrhotic animals, were restored to normal by either portacaval shunts or transposition. 7. Mortality occurring within 120 hours of the operation (36 per cent) was higher in the cirrhotic animals undergoing portacaval shunt. No deaths occurred among the cirrhotic dogs undergoing portacaval transposition. Furthermore, among the cirrhotic dogs none with portacaval shunt survived more than three months after operation, whereas all of the animals with transposition survived six months or longer.