ABH blood group antigenicity and unspecific immune response were evaluated in 31 patients with superficial transitional cell carcinoma. Of these patients 26% showed a reduced dinitrochlorbenzene (DNCB) reaction. There was no significant difference in the monocyte chemotaxis of patients with benign urological diseases and patients with superficial bladder cancer. A significant difference exists vs. patients with deeply infiltrating carcinomas. Twenty patients revealed a loss of ABH antigens on the initial tumor. During the follow-up of at least 1 yr, patients with negative DNCB skin test, reduced monocyte chemotaxis and negative specific red cell adherence test demonstrated a high rate of recurrent tumors; and 1 of 7 a progressive tumor developed.