The determination of the density distribution of erythrocyte population is one of the biological parameters used in several hemoglobin disorders. Many difficulties to obtain reproducible results between different laboratories lead to make a reference phtalate ester range for two hospitals. In this paper, the conditions of preparation and use of the method are described. Then, factors affecting determinations are discussed. Finally the authors give reference values in child and adult. This work forms the first stage of a standardized study of erythrocyte populations with hemoglobinopathies.