Abstract: Provided is a method for reproducible production of cytokeratin antigen immunogen. Cytokeratins from whole carcinoma cells are purified by preparative SDS-PAGE. Bands corresponding to cytokeratins 8, 18, and 19 are eluted from the gel, and these cytokeratins are digested to produce fragments in the size range of 10-50 Kd. The invention also relates to use of these fragments as immunogens for the production of antibodies. Furthermore, the invention relates to an immunochemical test kit to detect cancer of epithelial origin in body fluids. The kit comprises cytokeratin fragments produced by the method of the invention and antibodies to these fragments.