Most cells are thought to contain trace amounts of 2,3-diphosphoglycerate (DPG), as it acts as a cofactor in the interconversion of 2-phosphoglycerate and 3-phosphoglycerate by the glycolytic enzyme phosphoglyceromutase. DPG is synthesized from 1,3-diphosphoglycerate by the action of diphosphoglycerate mutase. Lowry et al.1 reported levels of 29 μmol DPG per kg wet weight brain tissue which is approximately 3 pmol per 108 cells, assuming that 1 g of brain tissue contains 109 cells. In contrast, erythroid cells contain 50-100 nmol DPG per 108 cells, depending on the species and the stage of development2. This is of the order of a 1,000-fold more DPG compared with non-erythroid cells. In red cells DPG concentration modulates the binding of oxygen to haemoglobin3,4. I show here that erythroid precurser cells also contain markedly raised levels of DPG.