The decapeptide 1-10 of hen's egg ovalbumin (OA), deduced from the known amino acid sequence (Gly-Ser-Ile-Gly-Ala-Ala-Ser-Met-Glu-Phe), was synthesized by Merrifield solid phase peptide synthesis with a yield of greater than 70%. The completeness of the insertion of amino acids during synthesis was monitored by the amino acid compositions of the peptide-resin, prior to coupling of the preceding residue. The linearity of the synthesis was supported by dansyl Edman degradation and detection of three NH2 terminal residues 5-dimethylamino-naphtheline-1-sulphonyl (DNS)-Gly, -Ser, -Ile, respectively. The peptide was purified by gel filtration chromatography and analytical reversed-phase high-performance liquid chromatography (HPLC). The homogeneity of the preparation was calculated both from the amino acid analysis and by integrating the peaks of HPLC to be greater than 83%. The antigenicity of the purified (P2) peptide could be detected by precipitation inhibition with the nephelometric technique. The decapeptide could also specifically react with functional structures on reaginic IgE molecule from the sera of individuals allergic to eggs, inhibiting its further binding to ovalbumin. An in-vivo experiment using direct skin test on two patients allergic to eggs showed no activity, rendering further testing unnecessary. The results suggest that the decapeptide of the NH2 terminal segment of OA encompasses an Ig-binding haptenic epitope.