The purpose of the present study was to assess a new quantitative urinary tumor marker for transitional cell carcinoma of the urinary bladder (TCC), measuring fragments of cytokeratin 8 and 18 in the urine (UBC). Urine samples of 355 individuals (77 healthy volunteers, 111 patients with benign urologic disorders, 167 patients with histologically proven bladder cancer) were examined for the presence of UBC antigen. Samples of all patients were obtained prior to therapy. Compared to healthy volunteers or patients with benign urologic disease, patients with TCC had significantly higher median urinary levels of UBC antigen (0 vs. 4.18 vs. 7.46 microg/g creatinine; p<0.001, and p<0.01, respectively). UBC antigen levels were positively correlated with tumor grade and stage. Patients with invasive TCC had significantly higher levels of UBC antigen than patients with superficial TCC (p<0.001). Elevated levels of UBC antigen were also found in patients with benign urologic disorders (median: 4.18 microg/g creatinine vs. 7.46 microg/g creatinine in cancer patients). Using a cutoff of 14.06 microg/g creatinine (corresponding to 95% specificity in the group of healthy individuals), sensitivity of UBC antigen ranged between 21.6% (pTa) and 75% (pT4). Overall specificity was 76.6%. Based on our data we conclude that the UBC antigen test in its current format is not clinically useful for detection of bladder cancer.