Growth and differentiation of urothelial cells in explant cultures of mouse urinary bladder were studied by means of scanning and transmission electron microscopy and lectin binding analysis. The proliferation and growth of epithelial cells over the cut edges of the explant and over the substrate began after explant attachment to the substrate was performed. The exogene EGF plays no important role in cell proliferation and epithelialization. The urothelial cells which are in contact with the stroma of the explants differentiate in a similar way as "in vivo". On the contrary, the urothelial cells which grow over the substrate exhibit only an epithelial stratification and are differentiated only partially.