The DNA content and S-phase fraction were measured by flow cytometry in 448 tumour biopsy specimens from transitional-cell bladder cancer (TCC). The samples were also analyzed for mitotic index, WHO grade and papillary status, and histological and flow cytometric data were then correlated to clinical behaviour of tumours during a mean follow-up period of 9.9 years. TNM classification, WHO grade, papillary status, mitotic index, DNA ploidy and S phase fraction were significantly interrelated. Twenty-four percent of tumours showed heterogeneous DNA indices when measured from multiple samples (measured in 94 cases). Of the histological parameters, independent predictors of progression in superficial tumours were the S-phase fraction and mitotic index. In superficial tumours, S-phase fraction and the mitotic index included all the available independent prognostic information in survival analysis, whereas in muscle-invasive tumours T category was the most important prognostic factor. The results suggest that DNA ploidy has no independent prognostic value in transitional-cell bladder cancer, whereas proliferation indices (SPF, mitotic index) are important prognostic factors. Accordingly, malignancy classification of papillary bladder tumours can be based on proliferation indices alone. Nodular tumours run an unfavourable course and their malignancy grading by flow cytometry or by mitotic index is not relevant.