This project will determine if volunteers treated with supplemental tyrosine during stressful phases of SERE training experience less degradation in cognitive performance and mood than volunteers treated with placebo. Tyrosine or placebo will be administered in a specially developed food bar provided to volunteers. The bar is part of a prototype of ration-component designed for use during assault operations. A between-subjects, double blind experimental design will be employed. Tyrosine, an amino acid found in most protein-containing foods, has been tested in hundreds of volunteers without adverse effects.