The of the erythrocyte biochemistry in 15 cases of hereditary elliptocytosis, shown and both before and after incubation with APHand an increase of G6PDH, NAPDH-GR, HK, PFK, ENOL, and LDH activities. A slight decrease in ALD and ATP-ase was also observed. The raised values of many enzymatic activities may be a consequence of hy-perhaemolysis and thus the presence of a young erythrocyte population containing an increased concentration of enzymes. The normal but low values of ATP-ase and the ALD deficiency may be the result of structural alterations of the erythrocyte membrane.