An increase in spectrin oxidation in a variety of erythrocytes displaying a tendency to vesiculate has been previously described. To explore this relationship in more detail, we have studied blood stored in citrate-phosphate-dextrose-adenine under blood bank conditions because, in this system, vesiculation occurs slowly. Vesiculation was quantitated by measuring acetylcholinesterase release, and the extent of spectrin oxidation was detected by using thiol-disulfide exchange chromatography. A strong correlation (r = .92) was found between the extent of spectrin oxidation and vesiculation when blood from five donors was analyzed at weekly intervals during storage. This strongly suggests that spectrin oxidation plays a role in the formation of spectrin-free vesicles, thereby limiting the shelf life of stored blood.