0767 Moderate to intense exercise and acute altitude (ALT) exposure can, respectively and collectively, increase oxidative stress resulting in cellular damage that can reduce physical and mental performance and negatively impact mood state. PURPOSE: To determine if antioxidant supplements will improve negative mood alterations in sealevel residents exercising during a sojourn at ALT. METHODS: 18 healthy informed men were equally divided into 2 groups matched for age (25 ± 2 yr, M ± SEM), weight (78 ± 3 kg), and VO2max (56 ± 2 mL/kg/min−1). In a double-blind fashion, the men were randomly assigned to a placebo (PLA) group (n = 9) or antioxidant supplemented (ANT) group (n = 9). After sea-level testing and 3 weeks prior to travel to ALT, volunteers consumed a gelatin capsule twice daily containing either antioxidants or placebo. The ANT consisted of 20,000 IU β-carotene, 400 IU α-tocopherol acetate, 500 mg ascorbic acid, 100 μg selenium and, 30 mg zinc. At sea-level (SL) and ALT days 3 and 10, subjects performed a maximum effort 720 kJ time-trial during which work rate was self-adjusted. Prior to the beginning of exercise, and 5 and 20 minutes postexercise, each completed the Feelings Profile, a 19-item short form (Jackson, et al., 1991) of the Profile of Mood States. RESULTS: There were no differences between groups at SL. On ALT day 3, Anger was significantly reduced (p = ≤0.05) in the ANT group compared to the PLA group at 5m post-exercise. On ALT day 10, Confusion and Global moods were lower in the ANT group (p = ≤0.05) than in the PLA group at 5m post-exercise. There were no differences between groups 20 minutes after cessation of exercise. CONCLUSION: These data suggest antioxidant supplementation improves negative mood alterations resulting from the combined effects of altitude exposure and exercise. Further investigations are necessary to identify the specific causal mechanisms. Supported by: The Borgenicht Program, The Jeffress Trust and, the DOD