The blood flow in an experimental adenocarcinoma in the rat liver was determined with the Xe-133-washout technique before and after hepatic artery ligation (HAL). There was an initial reduction of the washout of 50%. This was further reduced after 1 day by 50%, which was maintained for 7 days. Seven days after HAL or sham procedures the Xe-133-washout was of similar magnitude in the liver tumours, although after the sham procedure the tumours were larger (3.4 g vs. 1.5 g). The estimated tumour blood flow was then approximately 0.04 ml x min-1 x g-1. The influence on normal liver parenchyma of HAL was a reduction at 30 minutes, which was maintained for 7 days. Postacton(R)-a synthetic vasopressin-did not influence the Xe-133-washout in normal liver parenchyma in non-tumour, as well as in tumour-bearing animals. There was no influence of Postacton(R) on the Xe-133-washout in the liver tumours. Thirty minutes after HAL Postacton(R) gave a reduction of blood flow in normal liver parenchyma of tumour-bearing animals, which is thus only from the portal vein. In tumours Postacton(R) did not significantly reduce the tumour blood flow immediately after HAL.