BACKGROUND: Antitumor antibodies have traditionally been made to whole tumors or tumor extract. The use of defined synthetic antigens would be desirable for producing monoclonal antibodies. PURPOSE: Our purpose was to determine if antipeptide antibody to MUC2 had antitumor activity and specificity. METHODS: A 29-amino-acid peptide to MUC2 was synthesized and monoclonal antibodies were produced after immunizing BALB/c mice with peptide-keyhole-limpet hemocyanin in complete Freund’s adjuvant, and the monoclonal antibodies were tested on peptides and human tissues. RESULTS: CCP31, CCP37, and CCP58 monoclonal antibodies were produced using MUC2 MI-29 (KYPTTTPISTTTMVTPTPTPTGTQTPTTT) containing one repeat unit of 23 amino acids and part of the next repeat of four amino acids. These antibodies reacted with the MUC2-derived peptide but not with MUC1- or MUC3-derived peptides. One of the monoclonal antibodies, CCP58, reacted strongly with human colon cancer and normal intestine in both fresh and formalin-fixed tissues; two other antibodies, CCP37 and CCP31, reacted only with fresh human tissues of normal colon and malignant colon tumors by immunoperoxidase staining. In addition, CCP37 and CCP58 reacted strongly with human gastric cancer; all antibodies reacted weakly with human salivary gland, and none reacted with tissues from normal human lung, kidney, stomach, pancreas, or endometrium. By analysis of mucin molecules by Western blotting, the antigen detected by monoclonal antibodies CCP37 and CCP58 was found to be of a high relative molecular mass (520 kd). CONCLUSIONS: Anti-MUC2 peptide antibodies appear to be relatively tissue specific and represent a new method of producing antitumor antibodies.