(1) There is a significant decrease of ATPase activities in red cell membranes with increasing age of the donor. (2) A comparison of blood groups A and O relates the higher ATPase activities of young donors to blood group A. (3) Membrane ATPase activities reveal an age-dependent decrease in young and old donors with blood group A. (4) There is an age-dependent decrease of the N-acetylneuraminic acid concentration of glycophorin. (5) The galactose content of glycophorin only increases in blood group A. (6) There are no age-dependent changes of the exposed galactose. (7) The experiments so far reveal an increase of IgG absorption to old glycophorin