The present study was made on the constitution of Heinz bodies in the red blood cells in order to elucidate the genesis of the bodies. Heinz bodies which were formed in the red blood cells incubated with o-aminophenol, were separated, and analytically examined for their constitutive substances. The analysis was carried out to identify their staining properties with fluorescence staining, and to determine their constitutive substances using column chromatography. As a result of the experiments done in this study, it was concluded that the major part of Heinz bodies are composed of a substance, being formed by denaturation of hemoglobin, which shows a hemochromogen-like absorption spectrum after the treatment with NaOH and Na2S2O4.