OBJECTIVE The limitations of cytology and the invasiveness of cystoscopy for detecting bladder cancer generate increasing interest in noninvasive, urine bound diagnostic tools. We assessed the diagnostic value of the newly developed immunocytochemical test, Immunocyt, which detects cellular markers specific for transitional cell cancer in the voided urine of patients with bladder cancer. METHODS Participating in our prospective study were 264 consecutive patients with a mean age of 65.9 years, including 114 in whom symptoms were suggestive of bladder cancer and 150 who were being followed after complete transurethral resection of superficial transitional cell carcinoma. Voided urine specimens were evaluated by standard cytology and the Immunocyt test, which traces the monoclonal antibodies M344, LDQ10 and 19A211 against transitional cell carcinoma in exfoliated urothelial cells. In all cases cystoscopy was subsequently performed and any suspicious lesion was evaluated by biopsy. RESULTS Histologically proved transitional cell carcinoma was found in 79 patients. Immunocyt with cytology had 89.9% sensitivity overall (84, 88 and 96.5% in grades 1 to 3 disease, respectively). A total of 34 (43%), 3 (3.8%) and 34 (43%) cases were positive on Immunocyt only, cytology only and both evaluations, respectively. In 8 cases (10.1%) both tests were negative. Overall Immunocyt only was 86.1% sensitive (84, 84 and 89.6% in grades 1 to 3 disease, respectively) and 79.4% specific. Overall cytology only was 46.8% sensitive (4, 52 and 79.3% in grades 1 to 3 disease, respectively) and 98.2% specific. CONCLUSIONS Immunocyt is a noninvasive, highly sensitive test for detecting transitional cell carcinoma of all grades and stages. When combined with conventional urinary cytology, it may replace cystoscopy in select patients, especially in followup protocols of low grade transitional cell carcinoma.