Recently numerous defects of erythrocyte membrane proteins have been described in hereditary hemolytic anemias. An exact biochemical characterization of some different types of hereditary spherocytosis, hereditary elliptocytosis, hereditary pyropoikilocytosis and the hemolytic anemias with increased cation permeability (hereditary stomatocytosis) is possible after analysis of membrane proteins with SDS-polyacrylamide gel electrophoresis, quantitative determination of spectrin, the relation of dimeric to tetrameric spectrin, and partial tryptic digestion of the spectrins. The known clinical heterogeneity of the mentioned disorders is now partially explained by the different biochemical defects of the erythrocyte membrane. In classical hereditary spherocytosis a close relationship between erythrocyte spectrin content and clinical severity has been found. The clinical manifestation in hereditary elliptocytosis and hereditary pyropoikilocytosis mainly depends on the functional disturbance of variant spectrins, especially their ability to form tetramers, i.e. their ability for self-association of the spectrin chains. In the hydrocytic form of stomatocytosis a deficiency of the integral protein band 7.2b has been documented. Besides the analysis of erythrocyte membrane proteins the classical methods used in the study of congenital hemolytic anemias cannot be missed. Signs of increased hemolysis, erythrocyte morphology, osmotic fragility, autohemolysis, heat and mechanical stability of the erythrocyte membrane, intracellular cation concentration and studies of other family members, are indispensable prerequisites for classification, prognosis, and indication of therapeutic efforts, especially splenectomy.