Fetal hemoglobin (Hb F) was more markedly and rapidly broken by ascorbate and hydrogen peroxide, which was enzymatically generated, than adult hemoglobin (Hb A) . Adenosine triphosphate accelerated the hemoglobin degenerative action of ascorbic acid, but the effect of ATP was more marked in Hb A than in Hb F. The oxidation of oxyhemoglobin to methemoglobin by ferricyanide proceeded more rapidly in Hb F than in Hb A, while the oxidation rate of Hb by ascorbate and enzymatically generated hydrogen was not different between Hb F and Hb A. The results suggested that the faster breakdown rate of fetal hemoglobin by ascorbate is another characteristic of fetal hemoglobin which is resulting from its subunit difference from that of adult hemoglobin.