Hepatic blood flow in tumor and nontumor regions was studied in four patients with hepatocellular carcinoma and in 16 patients with metastatic liver tumors. The regional hepatic blood flow was measured with the tissue clearance of 133Xe delivered through the implantable drug infusion system. The regional hepatic arterial/portal blood flow ratio was also measured by means of intravenous injection of 99mTc-stannous phytate. Mean hepatic arterial blood flow ratio of tumor regions was higher than that of nontumor regions (81.83 +/- 24.55% vs. 46.64 +/- 20.05%; p less than 0.01). This result suggests that hepatic arterial blood flow is increased in tumor regions of the liver. In tumor regions, the regional blood flow of the hepatic artery was inversely correlated with the mass reduction rate. In the lesions that showed a higher mass reduction rate by the continuous drug infusion treatment, the endothelial damage of the arterial wall and tumor necrosis seem to decrease blood flow. From this study, measurement of regional hepatic blood flow and hepatic arterial/portal blood flow ratio may be useful to evaluate the effectiveness of treatment for hepatic tumors.