In a prospective, critical appraisal of simultaneously collected cystoscopic urine and bladder cancer washing for the evaluation of patients with bladder cancer little consistent difference in cellular yield or preservation could be documented between the 2 techniques. Diagnostic cells usually occurred in both types of specimens but in 20 to 30 per cent of the cases they could be identified only in cystoscopic urine. Over-all, 13.1 per cent of the cancers would have been missed had cystoscopic urine not been examined cytologically. Although bladder washing alone has a greater diagnostic yield than cystoscopic urine alone urine remains a valuable source of diagnostic information and should be evaluated, even when simultaneously collected bladder washings are available.