Cellular DNA cytometry is commonly used to assess the prognosis of bladder tumours. Measurements are made mainly on voided urine or irrigation fluids by flow or image cytometry. In order to determine whether this material is really representative of the bladder tumour, we compared DNA assessments of bladder washings and tumour imprints from the same patients using image cytometry on Feulgen-stained preparations. DNA aneuploidy was found in 41.0% of the washings, 42.6% of the imprints and 49.2% of the patients if both samples were considered. If DNA histograms are classified into three groups (diploid, diploid+aneuploid, aneuploid), a 70% concordance rate is obtained between washings and imprints. In 15% of the cases, an aneuploid population was found in both samples, but in different proportions. In the latter 15%, an aneuploid population was found in one sample but not in the other; this discrepancy, which is probably due to poor tumour exfoliation or to tumour heterogeneity, is of clinical significance since it indicates the importance of making DNA assessments on both washings and cells directly obtained from the tumour.