The prognostic value of cytometric DNA parameters and their possible influence on the planning of treatment were investigated in 44 patients with transitional carcinoma of the urinary bladder (17 G1 tumours, 15 G2 tumours, 12 G3 tumours) as compared with normal urothelium of 7 patients. The nuclear DNA content was measured by scanning cytophotometry in Feulgen stained cytological smears. A statistically significant correlation was found to exist between the combination of the DNA parameters stem line quotient, 5c exceeding rate and DNA malignancy grade and the appearance of recurrences. A discrimination of a low grade and a high grade tumour group was based on this result within the G1 and the G2 transitional carcinomas as well. All patients with a carcinoma classified as low grade were recurrence-free within an observation period of more than 10 years. Further studies should clarify if this group can be treated without a topic chemotherapy after transurethral electroresection in contrast to the high grade group in which a topic chemotherapy is necessary.