A survey of hemoglobinopathies which was carried out in the Takamatsu district during the period from January to August 1979 detected six families with abnormal hemoglobins. Approximately 6010 inhabitants were screened.Three of these families had the same new Hb variant (Hb Takamatsuβ120 Lys→Gln) that has not been previously reported.Existence of a blood relationship among these three families could not be established even after careful family studies.This abnormal hemoglobin was not associated with adverse symptoms and gave normal hematologic findings in the carriers.The isopropanol test was negative, oxygen affinity was within the normal range, and biosynthetic ratio in reticulocytes was around 1.0.One of the difficulties in the structural analysis of this hemoglobin was related to complete superposition of abnormalβXT-12b,13 on aβT-8.9 peptide in the fingerprint of the trypsin digest of aminoethylated aberrantβXchain. This was overcome by collection of abnormal tryptic 3 core (βXT-10-13) from unmodifiedβXchain, and subsequent digestion by chymotrypsin. Edman analysis of the chymotryptic peptides thus obtained successfully confirmed the substitution to beβ120 Lys→Gln.