The multiform biology of superficial bladder tumors, both morphologically and evolutively, and the lack of reliable predictors of progression have led the authors to study the Ag-NOR proteins as a new marker of these tumors. It is well known that particularly the low-grade superficial tumors frequently relapse on the same histologic and proliferative module. Their potential of progression is probably present at the time of the first manifestation of the disease or it can show itself along the relapsing evolution with classic modifications translating the cellular dedifferentiation. The NOR index, set up by the authors, has several advantages; firstly, it corresponds to a functional value of normal and neoplastic cells; secondly, it can be used also with paraffin blocks. Another advantage is the semiautomatic lecture, reproducible also in the urinary cytology, mainly of low-grade tumors, reducing the number of false-negatives. The conclusion of the study of 38 cases of superficial bladder cancer has induced the authors to believe that an increased NOR index is a reliable ‘marker’ of their progression. Therefore, the authors suggest the use of the NOR activity for the surveillance of the urothelial disease and for a more logical therapeutic strategy.