Human red cell sugar transport shows profound changes upon cellular aging.' As the human erythrocyte glucose transport protein shares more than 98% primary, structural homology with the rat and rabbit brain glucose transport can be isolated from human red cells in large (mg) quantities and, owing to the relative ease of manipulation of red cell contents by forming resealed ghosts, erythrocyte sugar transport may provide a useful experimental model for the study of the effects of the aging process on a protein-mediated membrane process. In this short paper we examine how the catalytic activity of the human erythrocyte glucose transport protein is modified by intracellular ATP and calcium, by extracellular calcium, and by the physical and compositional properties of its resident membrane bilayer.