From the archive of BB Biocyt company, 32 urinary bladder carcinomas (urothelium carcinomas, UC) and 7 cases of chronic cystitis were selected and examined in semiserial sections for the following antigens: 1) cell proliferation marker Ki-67 (expressed in the nuclei), 2) cell cycle regulator p16/INK4a polypeptide (expressed in the cytoplasm and nuclei), 3) urothelium marker p63 (expressed in the nuclei), 4) cytokeratin 7 (CK7). 5) cytokeratin 20 (CK20) and 6) high molecular weight cytokeratin (HMWCK). Invasive urothelium carcinomas showing a high grade dysplasia (invasive HG UC) comprised over the half (20 out of 32) of the investigated tumours. Microinvasion to lamina propria (seen in three HG papillary carcinomas) was regarded as an early infiltration even when the position of muscular layer could not be determined. Classical invasion across the urinary bladder wall and/or to surrounding tissues was found in 17 cases of low-differentiated HG UCs. The rest (9 out of 32 neoplasms) were either non-invasive papillary carcinomas of high (non-invasive HG UC, 5 cases) or low malignant potential (noninvasive LG UC, 4 cases). Finally, 3 cases were papillary urothelium neoplasms of low malignant potential (PUNLMP). HMWCK was present in all invasive tumours, whereas the frequency of other urothelium markers ranged from 65 to 88 %. Nevertheless, at least two markers were expressed in each invasive tumour. Staining for Ki-67 antigen was positive in over 50 % of the nuclei of HG UCs, while in the LG UCs, the frequency of positive Ki-67 staining did not exceed 25 %. In PUNLMP, the positive rate of Ki-67 stained dysplastic cells was below 10 %. The staining for p16 antigen did not correlate with the degree of dysplasia within urothelium tumours. For routine diagnostic, we recommend to combine the Ki-67 staining with detection of HMWCK. In cases of chronic cystitis, which developed urothelial hyperplasia and/or squamous metaplasia, the presence of p63 antigen was a relevant marker confirming the urothelial origin of the altered transitional cells (Tab. 6, Fig. 4, Ref. 69).