Multiple genes coding for human mucins have been identified (MUC 1-5) and here monoclonal antibodies (MoAb) to a gastrointestinal mucin--MUC2 are examined. The antibodies were made to a synthetic peptide representing a single repeat in the core protein of the variable number of tandem repeat region. Using the six-mer overlapping peptides synthesized on polyethylene pins, different binding sites were detected by five anti-MUC 2 MoAbs. These contained amino acids: STTT, PTT, GTQTP, TPTP and PTTT (one antibody), and TPTPT. The repeat region of MUC2 essentially is hydrophobic, but contain useful immunogenic sites. This information will be useful for studying the structure and function of MUC2.