An abnormal hemoglobin was suspected in a 70-year-old Japanese male with cerebral infarction and erythremia with high performance liquid chromatography assay of Hb A1c. The hemoglobin variant migrated to the anode more rapidly than Hb A. Structure determination studies, including amino acid analysis of the abnormal pep-tide and DNA sequencing of a partially clonedα-globin gene, demonstrated that it is a new hemoglobin variant which has been named Hb Kanagawa [α40(C5)Lys→Met]. This variant showed an increased oxygen affinity, decreased heme-heme interaction, and a lowered 2,3-diphosphoglycerate effect relative to normal.