We used the specific red cell adherence (SRCA) technique to detect the A, B,·cell surface antigen on 61 transitional cell carcinomas of the urinary bladder seen from 1979 to 1982 at the Urology Department of Kaohsiung Medical College Hospital. It was suggested in this study that the loss of surface antigen had good correlation with both the pathological grade and clinical stage of tumors. On the other hand, the patients deprived of the surface antigen were poorer in prognosis than those with positive surface antigens. Among the four groups of A, B,·and AB patients, patients with blood group·had higher mortality rates, and more susceptibility to loss of the surface antigen. This study also demonstrated that the activation of surface antigen will reduce as the age increased. Of 11 patients with recurrent stage A tumors in this study, 8 had positive surface antigen and 3 had negative surface antigen. In 8 cases of positive surface antigen, 1(13%) subsequently developed an invasive tumor. In contrast, 2 (67%) among the 3 negative surface antigens developed invasive tumors and the statistics showed significant differences (p < 0.05). Consequently, the SRCA technique may be valuable for predicting malignant potential in early stage cancer of the bladder.