In order to seek possible changes in Y-body frequency in transitional cell tumours, urinary sediments were examined from patients with tumours as compared with those without. A tendency to lower Y-body counts with increasing malignancy was found. Thus when comparing with the results of routine cytology examination those classified as group 3 and 4 had significantly lower Y-body counts than those without tumour cells. Furthermore, those with tumour cells and a tumour ('true' positives) had significantly lower Y-body counts than those with "tumour cells' but without a tumour ('false'-positives). In the tumour group those showing invasive growth had a lower Y-body count than those without. These results indicate that some possible benefits could be achieved if this method is applied to routine use. Polymorphonuclear leukocytes in urine were also examined. The results seemed to indicate a decrease in Y-body count also in these cells in patients with transitional cell tumours. The detection of Y-bodies, in polymorphonuclear leukocytes is, however, difficult, and further studies are necessary for definite conclusions. There were only a few false-positives (females with Y-bodies).