AIMS: To evaluate the expression of bcl-2 in transitional cell carcinoma (TCC) of the bladder; to compare bcl-2 expression with clinicopathological findings, p53 immunoreactivity, proliferating cell nuclear antigen (PCNA) expression, 2c deviation index (2cDI), 5c exceeding rate (5cER), and the mean nuclear area (MNA). METHODS: Cystectomy specimens from 77 patients with untreated, non-metastatic TCC of the bladder were studied. Expression of bcl-2, p53 and PCNA was detected immunohistochemically using the following monoclonal antibodies: bcl-2/124, DO-7 and PC10, respectively. Nuclear DNA content was analysed using static cytometry. RESULTS: Bcl-2 was expressed in 19 (24.7%) of 77 TCCs and in 74 (96.1%) of 77 normal samples of transitional epithelium (taken from normal tissue adjacent to the tumour in each case). In all cases, bcl-2 immunoreactivity was more intense in normal transitional epithelium than in TCC. In normal transitional epitehlium and superficial TCC bcl-2 immunoreactivity was observed at the basal layer, and not at the invasive front. Bcl-2 immunoreactivity was invesely correlated with histological grade and p53 immunoreactivity, and was not correlated with the pT category, disease progression, PCNA expression, 2cDI, 5cER, and the MNA. No significant correlation was found between bcl-2 expression and overall survival. CONCLUSIONS: Bcl-2 expression in TCC of the bladder seems to be associated with a less aggressive phenotype and does not play an important role in tumour progression.