A hybridoma 1 G 10 clone was derived from fusion between SP 2/0- Ag14 myeloma cells and spleen cells of BALB/C mice immunized with the soluble Noridet P40 extracts from a human colonic adenocarcinoma cell line SW 620. The 1 G 10 clone was identified to be able to produce monoclonal antibody of IgG1 subclass which had sufficient titer for immunoreactivity to both extracts from SW 620 cells and surgical colonic carcinoma tissues, but no immunoreactivity to both extracts from normal adult colorectal tissues, mixed human lymphocytes and normal human serum (NHS) as well as carcinoma embryonic antigen (CEA) by enzyme-linked immunosorbent assay (ELISA). By affinity column on Sepharose 4 B coupled with 1 G 10 IgG, colonic carcinoma-associated antigen (CCA) was purified from SW 620 cell extracts and thoracic ascitic fluid of a patient with lung adenocarcinoma. Western blotting analysis with 1 G 10 IgG demonstrated that one immunoreactive bands corresponding to 55 Kd molecule was observed in the samples of ascitic fluid and SW 620 cell extracts. The 55 Kd band could be stained with Alcian blue. The immunoreactivity of CCA to 1 G 10 antibody could be abolished completely by the treatment of the antigen with NaIO4 and proteinase K. These results indicated that the determinants of CCA reacted with 1 G 10 monoclonal antibody are probably both present in polysaccharide and protein part of the molecule. The specificity of anti-CCA 1 G 10 monoclonal antibody and its possible application for clinical oncology were discussed.