This paper reports upon the physiological monitoring of stress effects from individual infantrymen during immersive combat related scenarios demonstrated during the Future Immersive Training Environment- Joint Capability Technology Demonstration (FITE JCTD). Immersive training environments provide the opportunity to expose infantrymen to some of the stressors that they may experience in theater. In theory, exposure to realistic stressors may provide a degree of inoculation to the stress of the environment before it is experienced in theater, leading to better performance under stress and a reduction in the long term effects of combat stress. The goals of this study were to 1) identify whether the FITE immersive environment could provide a level of stress that could be measured physiologically, and 2) determine whether physiological measures could be used to objectively measure presence - or a sense of being in the environment rather than the sense of watching it. During this study Army and Marine Corps infantry squads participated in multiple virtual scenarios. Each participant wore an Expedition Dismounted Infantryman (ExDI) suit which allowed him to control an avatar within a Virtual Battlespace 2 (VBS2) scenario. Individual movements and actions taken by the participants were replicated by their avatars within the scenario. Each participant also wore a Threat-Fireâ„¢ system that provided negative feedback (electrical shock) to their thigh should they be shot or killed in some manner (e.g., IED, fall off building) during a scenario. Heart rate (HR) was collected from members of four squads (2 USMC, 2 USA) during each of the four scenarios. HR and HR variability were used to identify changes in stress level experienced by each infantryman throughout each scenario and were correlated to perceived level of readiness (Cooper's Color Code). Individual HR data was also correlated to scenario event time markers (e.g., sniper shot) to denote individual level of presence, and was correlated to subjective measures of perceived realism for each scenario.