An unusual case of bladder carcinoma is presented. The cystectomy specimen contained one large tumour with the histological picture of a poorly-moderately well-differentiated squamous cell carcinoma and another small tumour with poorly-differentiated transitional cell carcinoma. Besides, widespread areas of carcinoma in situ were seen. Random biopsies from the bladder and from the tumours were independently examined, histopathologically and by flow-cytofluorometric DNA-analyses. The degree of ploidy was found to be quite different between the two tumours. In areas of carcinoma in situ different aneuploid cll lines were indicated. Altogether five different aneuploid cell lines were found. There was a good correlation between the histopathological assessments and the DNA measurements: Carcinoma in situ corresponding to aneuploidy and various degrees of atypia corresponding to diploidy. In tumour metastases from several organs, only one aneuploid cell line was found. This cell line did not correspond to those found in the tumours.