Extracorporeal dialysis in uremic subjects produces erythrocyte alterations on energetic and redox metabolism. On this basis, we have tried to verify a fundamental parameter for the integrity of the red blood cell namely the glutathione content both in the oxidized and reduced form. Comparisons were made between two groups of subjects (similar in age, sex and number). One group consisted of uremic subjects undergoing dialysis and the other in healthy controls. As well as a slight increase in reduced glutathione (GSH), an accumulation of oxidized glutathione (GSSG) was found which, in postdialysis patients, reached values up to 3 times higher than in controls. This means a lowering in the ratio GSH/GSSG. There was also a decrease in total Mg(++)-ATPase activity, significantly found in erythrocyte ghosts of postdialysis patients. The hypothesis of a reduced efflux of GSSG as well as an increase in its formation speed (activation of glutathione peroxidase) is taken into consideration.