1. Oxidized glutathione reacts or interacts with some erythrocytic enzymes (glucose 6-phosphate dehydrogenase, EC 22.214.171.124, aspartate aminotransferase, EC 126.96.36.199) but not with some others (lactate dehydrogenase, EC 188.8.131.52). 2. GSSG does not diminish the activity of any of these enzymes and is therefore not responsible for the decreased enzyme activities associated with older erythrocytes. 3. It may be that the reaction of aspartate aminotransferase with GSSG is the cause for the more rapid anodic electrophoretic mobility of this enzyme derived from human erythrocytes when compared with the mobility of the same enzyme from other human tissues. 4. A reinterpretation of some related, previously published, data with regard to the electrophoretic mobility of the above-mentioned enzymes from young and old erythrocytes is presented.