Purpose: Urinary cytology and cystoscopic exam are effective methods for diagnosis of transitional cell carcinoma(TCC). But the former shows drawbacks such as the need for a well-trained examiner, and wide imprecision related to the variability of microscopic exam the latter is an invasive method. UBC™ test detects the epitope on specific cytokeratin fragments released from epithelium of bladder cancer by immunoradiometric assay. We compared UBC™ test with urinary cytology for diagnosis of TCC to evaluate the utility of UBC™ test. Materials and Methods: Eighty-four patients with hematuria were included in our study. UBC™ tests (IDL Biotech, Sweden) were assayed in mid-stream urine according to the ordinary assay protocol. Nineteen patients were confirmed as TCC by cystoscopic examination and underwent transurethral resection (Group A). Other patients had various benign urinary tract conditions (Group B). Samples were considered positive as the UBC™ concentration was greater than 12 μg/L. Results: UBC levels were significantly different between group A (95.9±166.4 μg/L) and group B (19.2±85.6 μg/L) (p<0.001). Sensitivity for diagnosis of TCC was 89.5% (17/19) in UBC test and 47.4% (9/19) in cytology (p<0.05). Specificity for diagnosis of TCC was 81.5% (53/65) in UBC test and 100% (65/65) in cytology. UBC test was significantly more sensitive in stage Ta, T tumors (84.6 vs 38.5%, p<0.05) and in grade I (83.3% vs 16.7% p<0.05) than cytology. UBC test showed a tendency to be more sensitive as the grade was higher (83.3% in Grade 1.90% in Grade II and 100% in Grade III). Conclusion: UBC™ test could be a useful method in distinguishing TCC from other benign genitourinary diseases. Moreover, UBC™ test could be an especially valuable marker for diagnosis of TCC in patients with early TCC of low grade TCC compared to urinary cytology. Therefore, mbined use of UBC™ test in association with cytology is helpful to overcome the limited sensitivity of cytology. (Korean J Nucl Med 200135:192-197)