Negative selenium and zinc balances occur after major trauma, potentially compromising antioxidant defenses. The aim of this study was to determine if micronutrient supplementation could modulate the blood antioxidant status. 32 patients admitted to surgical ITU with major trauma were randomized to receive either selenium alone, selenium plus copper, zinc and tocopherol, or placebo for 5 days after injury. Blood samples were collected on days 0, 1, 2, 5, 10 and 20 and analyzed for plasma selenium, copper, zinc, tocopherol, glutathione peroxidase and total antioxidant capacity (TAC), and for erythrocyte antioxidant enzymes. Plasma selenium and tocopherol concentrations were low on admission, but increased significantly (p = 0.001) with supplementation, whereas there was an early significant fall in TAC (p < 0.002) in the selenium supplemented groups. Plasma glutathione peroxidase activity increased significantly between days 2 and 5 with supplementation (p = 0.02), but erythrocyte enzyme activity was unaffected. The unexpected early fall in plasma TAC with supplementation may reflect mobilization of antioxidant defenses. O 2001 Elsevier Science Inc. All rights reserved.