Transfusion of allogeneic blood products is associated with adverse reactions and complications. Some of the negative effects of RBC transfusion are associated with the storage lesion. The importance of RBC oxidative damage in the storage lesion is not well documented. We monitored the storage-induced membrane protein oxidation in CPDA-preserved non-leukodepleted RBCs units from five blood donors in the course of the storage period, as assessed by protein carbonylation levels estimation. Carbonylated protein content was determined following 2,4-dinitrophenylhydrazine derivatization and SDS-polyacrylamide gel electrophoresis coupled with Western blotting. Immunoblotting with dinitrophenol-specific antibody revealed increased RBC membrane protein carbonyls with prolonged storage in CPDA units. This finding supports the idea of oxidation as a part of the storage lesion.