Mitotic indices and nuclear volumes were determined in 10 papillomas, 20 grade I, 20 grade II and 20 grade III papillary carcinomas of the urinary bladder. The mean mitotic indices were 1.22% in papillomas, 2.77% in grade I carcinomas, 8.2% in grade II carcinomas and 15.25% in grade III carcinomas. The nuclear volumes showed a gradual shift to larger values paralleling the histological degree. It is suggested that these objective parameters might be especially useful for the cytological assessment of exfoliated tumor cells.