Purpose: We evaluated the diagnostic performance of the new noninvasive bladder cancer test on voided urine samples from patients with transitional cell carcinoma compared to symptomatic and asymptomatic controls. Materials and Methods: Urinary bladder cancer antigen was measured in urine from 86 patients with active transitional cell carcinoma of the bladder (group 1), 76 patients free of transitional cell carcinoma as confirmed by cystoscopy at followup (group 2), 25 patients with other benign urological diseases (group 3), 25 patients with other malignant pathological conditions (group 4) and 30 healthy subjects free of urological diseases (group 5). Results: Mean urinary bladder cancer antigen concentrations were 104.84, 4.57, 11.79, 48.87 and 1.38 mu g./l., for groups 1 to 5, respectively, which was statistically different (p = 0.00005) except for groups 1 and 4 (p = 0.187). Sensitivity was 87.0% (95% confidence interval 79.2 to 92.7) and specificity was 86.8% (77.1 to 93.5%), and both were optimized by receiver operating characteristics plot analysis at a threshold value of 9.74 mu g./l, using asymptomatic (group 2) compared to known cancer (group 1) cases. Conclusions: Urinary bladder cancer antigen might have a role as a potential tumor marker for diagnosing transitional cell carcinoma of the bladder.