Oxidative stress is one of the suggested mechanisms in major depression.

To determine the oxidative and antioxidative status of plasma of patients with major depression and to investigate whether there is a relationship between the potency of oxidative stress and the severity of depression.

To determine the antioxidative status of plasma, total and individual antioxidant levels which are total antioxidant potential (TAOP), total protein, albumin, uric acid, vitamin C and total bilirubin were measured. To determine the oxidative status, total peroxide level of plasma was measured in patients with drug-free depressive patients and compared with those of controls. Per cent ratio of total peroxide to TAOP was evaluated as oxidative stress index (OSI).

Plasma TAOP and individual antioxidant levels were found to be lower in patients with depression than those of controls. On the contrary, the patients had high total plasma peroxide levels. OSI values of the patients were significantly higher than those of controls (P = 0.002), and a significant positive correlation between Hamilton Depression Rating Scale (HDRS) and OSI values was found (r = 0.54, P = 0.01).

The patients with major depression are exposed to oxidative stress, and OSI may be useful to reflect the severity of the disease.