Summary— Cell material from 100 cases of newly diagnosed bladder tumours was studied with rapid flow cytofluorometric DNA analysis. The degree of ploidy and the percentage of cells in the S-phase characterising the proliferation pattern of the tumours were determined from DNA histograms. The results were related to the tumour categories and to the histopathological grading of the tumours.

Approximately 40% of T1 tumours showed aneuploid DNA patterns, while in the other categories aneuploidy was found in almost all cases. With few exceptions, tumours of Grade 1 were found to be diploid and tumours of Grade 3 aneuploid. In tumours of Grade 2, two-thirds were diploid and one-third aneuploid.

In the group of aneuploid tumours the tetraploid cases exhibited the least malignant characteristics as judged by histological grades and tumour categories. The aneuploid non-tetraploid tumours increased in malignancy the more they deviated from tetraploidy. This might be explained by our observations of a positive correlation between the degree of ploidy and the degree of proliferation. The proliferation increased from 10% in tetraploid tumours to 20% in triploid and pentaploid tumours.