Various in vitro-aging procedures are introduced as an alternative to the difficult isolation of physiologically aged erythrocytes standing immediately before elimination. N-acetylneuraminic acid, ATP- and glutathione contents of these model cells are estimated and the kind and degree of membrane damage were characterized by the rates of phagocytosis and exovesiculation. Conclusions concerning molecular biological mechanisms of age-related processes were drawn by correlating biochemical data with the degree of membrane lesion. Alterations of spectrin (cross-linking, aggregation, rearrangement) seem to play the main role in all in vitro-ageing processes described here.