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Old human red blood cells (RBCs) have a reduced surface area with respect to young RBCs. If this decrease occurred through the release of vesicles similar to the spectrin-free vesicles that are shed in vitro under different experimental conditions or during storage, there would be no decrease of membrane-skeleton, but only of lipid bilayer surface area, during RBC ageing in vivo. However, we observed a decrease in spectrin and other membrane-skeletal proteins in old RBCs. Because RBCs contain components of the ubiquitin-proteasome system and other hydrolytic systems for protein degradation, we asked whether increased membrane-skeleton fragments could be detected in older RBCs. Four different anti-spectrin antibodies and an antibody anti-ubiquitin conjugates were used to analyse, by Western blotting, fragments of spectrin and other proteins in RBCs of different age separated in …