We examined the usefulness of factor analysis for the diagnosis of hepatocellular carcinoma by analysis of the data obtained by radionuclide angiography. The data could be separated into two factors, a hepatic phase (hepatic artery and portal vein) and an arterial phase (aorta and kidney). In patients with hepatocellular carcinoma, the factor of the tumor is included in the arterial phase, so that the cancerous region could be differentiated from the noncancerous region. The ratio of the radioactivity of the cancerous region to the noncancerous region was used to estimate the blood flow of the tumor region.