Results of cell kinetic analyses on transurethrally obtained material from urinary bladder are compared with parallel immunohistochemical tests on carcinoembryonic antigen (CEA) and tissue polypeptide antigen (TPA), performed on the same material. Labelling index increases from 1.4% in slight to 20% in marked urothelial atypia. CEA reaction in slight atypia is slight or moderate, slight, moderate or distinct in atypia, and moderate to distinct in carcinoma in situ. TPA always shows moderate to distinct reactions. Cell kinetically, urothelial carcinomas yield similar gradations. They were positive for CEA in 70% and for TPA in 100%. In GO and GI carcinomas, negative and slightly positive reactions predominate, poorly differentiated lesions yield predominantly distinct reactions. In all grades, TPA ranges from slight to distinctly positive. As in cell kinetic analyses, there is a relationship between differentiation grade and stage for CEA expression. This does not apply for TPA. The results permit us to draw conclusions on the different biological and histogenetical behavior of urothelial carcinomas. There are undoubtedly differences in the behavior of papillary-exophytical and solid invasive carcinomas in terms of both cell kinetics and immunohistochemistry.