KUMAGAI, R., NIITSU, H., KATSURA, I., NAKAYASHIKI, N. and KATSURA, S.A Case of a Newborn Infant with Hb M Iwate. Tohoku J. exp. Med., 1986, 150 (3), 337-343-Hemoglobin of a newborn infant who was suspected to hereditarily have Hb M Iwate was examined. The infant hemolysate was separated into five fractions by column chromatography on Amberlite CG-50, and two of these fractions showed absorption spectra corresponding with that of Hb M Iwate. Five bands were found after the isoelectric focusing of the hemolysate, and two of these bands were brown. The two Hb M fractions obtained by column chromatography was focused to the positions of the brown bands. One of these Hbs M corresponded with Hb M Iwate (α^M₂β₂) from an adult carrier of this trait, but the other was not found in adult hemolysates. The latter species of Hb M was shown to be composed of the abnormal α chain and the normal γ chain (α^M₂γ₂) by chain analysis, and was assumed to be specific for infants. A quantitative estimation of the hemoglobins in the infant hemolysate showed that there was no difference between the relative quantities of the fetal and adult forms of Hb M Iwate.