A new case of congenital stomatocytosis associated with haemolytic anaemia, increased autohaemolysis, abnormalities in the erythrocyte metabolism, increased osmotic fragility and shortened erythrocyte survival is dmcribed. Intracellular cation concentrations are abnormal: Red cell sodium is high, and potassium is low. The pump rate for monovalent cations is increased. K e y words: stomatocytosishaemolysisred cell cations