We have investigated age-related changes in the reliability of glutathione-related antioxidant enzyme defense in monkeys that differ in adaptive behavior. Activities of gluthatione reductase (GR), glutathione peroxidase (GSH-Px), and gluthatione-S-transferase (GST) and also lipid peroxidation products (TBARS) under basal conditions and under acute psycho-emotional stress were evaluated in erythrocytes of young (6-8 years) and old (20-27 years) female rhesus monkeys with depression-like and standard (control) behavior. We have found that young animals with depression-like behavior, in comparison with young monkeys of standard behavior, demonstrated higher activity of GR in basal conditions and no significant changes in response to acute immobilization stress. With aging the activity of GR increased in monkeys with standard behavior in basal conditions but retained the ability to increase under acute stress. At the same time during aging in monkeys with depression-like behavior GR activity did not undergo significant changes in basal conditions and did not change in response to acute stress. Moreover, old animals with depression-like behavior demonstrated reduced activity of GSH-Px. More pronounced disturbances in GR and GSH-Px activities in animals with depression-like behavior evidence a more marked decrease in the reliability of antioxidant enzyme defense of cells and lead to activation of lipid peroxidation that may be considered as an important factor of aging. Thus, age-related dysfunctions of the antioxidant enzyme system correlate with the type of adaptive behavior characteristic of animals.