Bladder tumor antigen (BTA) is a tumor marker isolated from the urine of individuals with TCC of the bladder. This antigen can be detected by the Tu-MARK BTA test, a simple and rapid slide latex agglutination test performed on freshly voided urine. Sensitivity and specificity of BTA were calculated, and the correlation with pathological grade, histological stage, and urinary findings were statistically evaluated (chi 2-test) in 110 patients (72 male, 38 female; age: 16-91, mean age 54.4) examined between September, 1989 and April, 1990 including 46 TCC of the bladder (primary 28, secondary 18; grade 1:10, grade 2:27, grade 3:9, pTis: 2, pTa: 2, pT1: 23, pT2: 5, pT3: 4, pT4: 2), and 64 benign diseases. Sensitivity was 45.6%, specificity was 60.9%. In bladder tumor cases a correlation was seen between BTA and stage (p less than 0.02), and between BTA and grade (P less than 0.05). The positive ratio was higher in T1-T4 (55.9%) than in Tis.Ta (p less than 0.02). A high positive ratio of BTA was seen in bladder tumor cases with hematuria (70%, p less than 0.01) and pyuria (86.7%, p less than 0.01). This method is easy and rapid and the values are highly correlated with stage. Therefore, it should be useful for not only screening but followup of bladder tumor. Furthermore, BTA in combination with urine cytology is a more useful way for diagnosing TCC of the bladder.