Chemotherapy of liver metastases is dependent on adequacy of tumor microcirculation. Attempts have been made, experimentally, to improve tumor blood flow with appropriate vasoactive agents. Capillary blood flow within intrahepatic Walker carcinosarcomas and normal liver were measured with a laser doppler needle probe. Tumor capillary blood flow increased briefly but significantly with intraportally administered epinephrine. This effect was blocked by phenoxybenzamine but not by propranolol. The response of capillary flow in normal liver to epinephrine was dose related, with decreased flow with higher doses, and slight increase with lower doses. Norepinephrine and phenylephrine produced brief increases in capillary flow in tumor and liver, and isoproterenol caused a decreased flow. In studies with injected silicone rubber (Microfil, Canton Bio-Medical Products, Boulder, CO) performed previously, and on electron microscopic examination, there was evidence of increased vascular filling within central areas of tumors after epinephrine. These studies suggest that the brief but potent effect of epinephrine on tumor capillary flow could be useful in improving delivery of chemotherapeutic agents to liver tumors.