Blood collected routinely from donors, and preserved with CPDA-1 anticoagulant (citrate, phosphate, dextrose, adenine), was investigated. The concentration of reduced glutathione, and glutathione peroxidase, glutathione S-transferase, glutathione reductase, superoxide dismutase, and catalase activities in erythrocytes, as well as the total radical-trapping antioxidant parameter in plasma were determined on days 1, 3, 7, 12, 16, 20 and 25 of storage. At the end of the study, a 30% decrease in the reduced glutathione concentration (P < 0.001) and decreases in glutathione S-transferase (over 20%, P < 0.001), glutathione reductase (over 8%, P < 0.01) and superoxide dismutase (over 10%, P < 0.001) activities in erythrocytes, together with up to a 30% diminution of total antioxidant activity in plasma (P < 0.001) were noted. Thus, during blood storage, glutathione-dependent antioxidant systems in erythrocytes and antioxidant defence in plasma are depleted. From the present study, a twelve-day period can be considered a safe storage limit. The sequence of events occurring in stored blood, leading to peroxidative injury in erythrocytes, is discussed.