An abnormal human hemoglobin was discovered in a woman living at Atago in Nagasaki and was designated Hb Atago.In the thin‐layer starch gel electrophoresis with Tris‐EDTA‐borate buffer, pH 8.6, the main component of this abnormal hemoglobin migrated towards the anode a little behind Hb F, and the minor abnormal component migrated to the same site as non‐hemoglobin protein did. These abnormal components were isolated by CM‐cellulose column chromatography. The hybridization method proved that the α chain of Hb Atago had the abnormality. The abnormal α chain was isolated by CM‐cellulose column chromatography in 8 M urea. The tryptic peptide map of the aminoethylated abnormal α chain showed that the abnormality existed in αT9. The abnormal αT9 was isolated and purified by high voltage paper electrophoresis. The abnormal chymotryptic peptides from αT9 were purified by high voltage paper electrophoresis and paper chromatography. The amino acid compositions of these peptides were analyzed.As a result, it was found that in Hb Atago, a tyrosine residue was substituted for the aspartic acid residue at α85 in the norma