After extraction in high salt buffers and Triton X-100, cytokeratin polypeptides could be isolated from normal epithelium and transitional cell carcinoma of the human bladder in the southwestern coast of Taiwan. The polypeptides were solubilized via lysis buffer, separated by two-dimensional gel electrophoresis, and identified by immunoblot. Five cases of normal epithelium expressed cytokeratin No. 5 (58 kd), 7 (54 kd), 18 (45 kd) and one case further expressed cytokeratin No. 19 (40 kd) in addition to the above cytokeratins. Combined patterns of cytokeratin polypeptides were observed among various Grades of transitional cell carcinoma of bladder. Comparing the patterns between the normal epithelium and the transitional cell carcinoma of bladder, 88% (14/16) of carcinomas expressed cytokeratin No. 8 (52.5 kd) and 63% (10/16) expressed No. 17 (46 kd), which were not seen in the normal epithelium. Some other cytokeratin polypeptides particular to carcinomas were No. 4 (59 kd), No. 10 (56.5 kd), No. 13 (54 kd) and No. 14 (50 kd) and were only present in less than 50% (ranging from 31-56%) of the examined specimens. Thus cytokeratin No. 8 and 17 could be helpful markers for diagnosis of bladder carcinoma.