1. The effect of anaemia and transfusion with adult blood on fetal 2,3-diphosphoglycerate levels was investigated by studying fetal blood from 45 normal pregnancies at 17–42 weeks of gestation and in 34 pregnancies complicated by erythroblastosis fetalis.
2. In normal fetuses, 2,3-diphosphoglycerate concentration was higher than in adults and did not change significantly with gestational age.
3. In erythroblastotic fetuses, there was a significant negative correlation between 2,3-diphosphoglycerate concentration and haemoglobin concentration.
4. When adult blood was transfused into the fetal circulation, 2,3-diphosphoglycerate concentration reached similar levels to that found in untransfused fetuses after allowing for the severity of anaemia.