The author performed immunohistochemical staining of blood group antigen (BGA), CEA, BMG, Leu-M1 and H-Ag on 43 patients with primary superficial bladder tumor to evaluate the malignant potential of bladder tumor. There were no obvious relationships among reactivities to BGA, CEA, BMG, Leu-M1 and H-Ag in identical tissue. Although BGA, CEA and Leu-M1 could be used individually as indicators of malignant potential, of the three, BGA was found to be most useful. Concomitant use of Leu-M1 with BGA might compensate for the disadvantages of BGA alone and make prediction of prognosis more objective. Then, a new evaluation criteria for detecting malignant potential of bladder tumor was proposed.