Keratin was found in more than 90% of transitional cell carcinomas of the bladder in the cytoplasma with polyclonal antibodies. Intensity increased with dedifferentiation. Cytokeratin was detected with monoclonal antibodies in more than 80%. Squamous cell carcinoma of the urinary bladder was always strongly positive for keratin and cytokeratin. CEA was found in 20% of G1 and 40% of G2 and G3 carcinomas of the urinary bladder. The prostatic epithelium markers PSA and PAP were always negative also Ca1.