In bladder cancer cell lines, CYP1‐activity was undetectable/low in basal PORlo T24 and SCaBER cells and higher in the luminal POR over‐expressing RT4 and RT112 cells than in differentiated NHU cells, indicating that CYP‐function is related to differentiation status in bladder cancers. This evidence concerns the gene CYP1A1 and urinary bladder carcinoma.