A retrospective study of DNA flow cytometry (FCM) in paraffin-embedded tissues of urinary bladder transitional cell carcinoma (TCC) was performed on 239 biopsy samples taken from 81 patients in the period from 1984 to 1994. 210 (87%) were analysable. Of these samples 21 patients had multiple biopsies taken from large tumours and/or bladder mucosa showing an endoscopically normal appearance. DNA-FCM results have been evaluated comparing ploidy and histopathological grade, clinical stage and different clinical status, i.e., first diagnosis, recurrence and patients who died from bladder cancer. Our results indicate that 'diploid' FCM correlated with a better prognosis, whilst DNA aneuploid correlated with malignancy and a poorer prognosis. There was a trend to an increasing incidence of DNA aneuploidy as the grade of the tumour rose and the proportion of biopsies with aneuploidy was significantly higher in malignant tissue samples, recurrences and in biopsies from patients who died from TCC than in other groups. In 12 patients from whom several biopsies were obtained, samples from recurrences had significantly higher DNA aneuploidy than those from the first diagnosis.