Erythrocyte 2,3-diphosphoglycerate (2,3-DPG) levels were measured in 26 cases of Cooley's anemia and 25 normal healthy infants and children. The mean value of 2,3-DPG in Cooley's anemia was 19.6 μmol/g Hb (S.D. 3.1 μmol/g Hb), and that in the control group was 14.7 μmol/g Hb (S.D. 1.9 μmol/g Hb). The former was significantly higher than the latter (P<0.0005). The increase in erythrocyte 2,3-DPG ... [Show full abstract] in Cooley's anemia is considered to be a compensatory mechanism for improving the tissue hypoxia in the disease.