The flowcytometric test measures the fluorescence intensity of intact red cells labelled with the dye eosin-5-maleimide, which reacts covalently with Lys-430 on the first extracellular loop of band 3 protein. In this study, red cells from patients with hereditary spherocytosis (HS) have produced a greater degree of reduction of mean channel fluorescence readings than those for other patient groups and normal controls. The predictive value of this test for membrane abnormality was compared with the results obtained from the fresh osmotic fragility test, incubated osmotic fragility test, fresh acidified glycerol lysis test and incubated acidified glycerol lysis test. The dye method is a reliable, speedy diagnostic test (2hours from sample collection to result) for HS with a sensitivity of 100% and a specificity of 95%. Thus it will serve well as a first line screening test for the diagnosis of hereditary spherocytosis in routine hematology.