Samples of bladder washings are frequently used to provide cellular material for flow cytometric DNA analysis. Since voided urine is a potential source of similar material, the aim of this study was to determine whether voided urine yields satisfactory specimens. We compared the qualitative results of flow cytometric DNA analysis of the cells in 53 specimens of voided urine and 109 samples of bladder washings; 45% (24/53) of urine specimens gave satisfactory DNA histograms compared with 93% (101/109) of bladder washings. This difference was apparent regardless of whether the bladder contained a tumour. It was concluded that bladder washings provide superior material for flow cytometric DNA analysis and that flow cytometric DNA analysis of freshly voided urine may have deficiencies which preclude its use in routine clinical practice.