The 2,3-diphosphoglycerate content of blood was determined by a bacterial NADH-linked bioluminescence measurement technique. The reaction conditions were chosen so that either an end-point or kinetic measurement was possible and easy to perform. Blood samples from twenty clinical patients were measured for their 2,3-diphosphoglycerate content using both luminescent and conventional spectrophotometric techniques. Correlation between the two methods was good and recovery for the bioluminescent method when adding a known quantity of 2,3-diphosphoglycerate was 95%. Luminescence analysis makes it possible to measure 2,3-diphosphoglycerate in just a few drops of blood taken from an adult's finger or from a baby.