Australia antigen (Au Ag) has been found in a higher frequency in patients with acute hepatitis, leukemia or Hodgkin’s disease as compared to normal subjects, in this study, 759 sera from 453 patients with advanced cancer were tested for Au Ag by the double radical immunodiffusion of Ouchterlony and by counter-electrophoresis. In addition, 40 patients with different non-neoplastic disease, 45 with malignancy of reticuloendothelial (RE) tissues, and 15 with viral hepatitis were tested for the presence of Au Ag. The Au Ag was found in 5 (1.1%) of the cancer patients, and in 3 (60%) of 5 patients with serum hepatitis. No Au Ag was found in any other sera tested. None of the 12 patients with hepatoma were found to have Au AG, while α-1-fetoprotein was found in the sera in 8 of the cases.