To evaluate urinary NMP22 dosage as a marker of urothelial tumours, we have selected a group of 90 patients (85 males and 5 females, mean age 66 years) with clinical suspicion of transitional cell carcinoma (TCC), with microscopic or macroscopic hematuria, flank pain, urographic abnormalities and dysuria. All the patients have been evaluated by urinary cytology, renal and bladder ultrasound, cystoscopy. When a bladder tumour has been detected, bladder biopsies and, when required, I.V.P., CT or retrograde pyelography have been performed. A urine sample has been collected between midnight and noon; all samples from patients who were undergoing invasive procedures such as cystoscopy, were collected before or at least 5 days after the procedure. The test has been performed according to ELISA NMP22 (Matritech) technique; the test is specific for the nuclear matrix protein/nuclear mitotic apparatus protein expressed by cancer cells. When performing the test, 30 patients presented macroscopic hematuria. 22 patients resulted to have benign urinary tract conditions, 65 patients had TCC and 3 patients had a final evaluation suspicious for TCC. The NMP22 values were respectively 7.1 +/- 4.7 U/ml, 21.9 +/- 21.0 U/ml and 16 +/- 8.0 U/ml. From our study the sensitivity of the test is 67% (with a threshold value of 10 U/ml) and 55% (with a threshold value of 20 U/ml), while the urinary cytology resulted to have a sensitivity of 26% (p < 0.05). The sensitivity of the test in relation to staging was as follow: Tis 66% with a mean NMP22 value of 23.3 U/ml, Ta 26% with a mean NMP22 value of 13.2 U/ml, T1 100% with a mean NMP22 value of 40 U/ml, T2 73% with a mean NMP22 value of 36.4 U/ml. The specificity of the test was 100% with a threshold value of 20 U/ml. When considering a threshold value of 10 U/ml, the NMP22 test has a sensitivity higher than cytology, especially in low stage TCC. Macroscopic hematuria does not affect its sensitivity; the diagnostic efficacy of the test is not increased by the association of urinary cytology. It has an important role in the diagnosis of residual disease after TURB and in the follow-up evaluation of bladder cancer patients, since its dosage is not influenced by inflammatory conditions of the mucosa. We believe therefore that NMP22 is useful in clinical practice.