Intra-erythrocytic concentration of 2,3-diphosphoglycerate is a major determinant of the oxygen affinity of hemoglobin. We report here the adaptation of its assay to a centrifugal analyzer, with use of a commercially available reagent. Results are calculated by using the reagent-blank-corrected absorbance change at 340 nm between 120 and 300 s for the samples and a 2.5 mmol/L standard. Under these conditions the standard curve is linear to 5 mmol/L. The compound in a 101-fold aqueous hemolysate is stable for several weeks at either -4 or -70 degrees C. Assay sensitivity and precision are excellent and results agree well with those by the corresponding manual method.