Ninety-four patients with transitional cell carcinoma (TCC) of the renal pelvis and ureter, including dysplastic lesions, were studied for p53 and bcl-2 protein expression by immunohistochemistry. Twenty-one patients were also studied for p53 gene mutations by direct sequencing and for bcl-2 gene rearrangement by Southern blot analysis. Overexpressed p53 protein was detected in 26 cases (27.7 per cent). bcl-2 immunostaining was observed in 21 tumours (22.3 per cent), including four cases with labelling for p53. Furthermore, the dysplastic lesions surrounding 19 p53-positive tumours also stained for p53. bcl-2 expression was also detected frequently in dysplastic lesions adjacent to 14 bcl-2-positive TCCs. Positive reactions of dysplastic lesions were also found adjacent to 37 bcl-2-negative tumours. p53 point mutation was detected in 6 of 21 cases. Five of the six cases were positive for p53 protein. blc-2 positivity was detected in 3 of 21 tumours, without bcl-2 gene rearrangements in the major breakpoint region. Overexpressed p53 protein was frequently detected in both high-grade (P < 0.05) and invasive tumours (P < 0.05). In three cases of p53-positive non-papillary invasive tumours, bcl-2 was found in non-invasive portions, but was not present in invasive areas. These findings suggest that overexpression (mutation) of p53 and/or bcl-2 protein may be early events in tumourigenesis and that p53 alterations in particular are essential for the maintenance of a malignant phenotype in tumour development.