After resolution of pepsin-treated ovomucoid (OM) with gel filtration and reverse phase HPLC, we determined the OM fractions which showed IgE-binding activity by means of direct radioallergosorbent assay (RAST) using polyvinyl 96-well plate. Fifteen subjects with high IgE antibody titers to OM were divided into two groups with positive (n=8) and negative (n=7) results to double-blinded placebo-controlled food challenge with freeze-dried egg white antigens. The sera from positive challenge group showed significantly high IgE-binding activity to fraction No. 23 and No. 38 from gel filtration (Bio Gel P-30 column), however those from negative group showed significant binding to none of fractions. No. 23 fraction which was recognized most frequently by patients' sera was subjected to further analysis with reverse phase HPLC (C18 column). No. 18 fraction showed binding activity to IgE antibodies from patients with positive challenge results. N-terminal amino acid sequence of the fraction No. 18 corresponded to the peptide which began with No. 134 of amino acid residues of OM. In conclusion this peptide was derived from the third domain of OM and may have an important role in egg-white hypersensitivity.