Biopsychological research has frequently (but not always) indicated that patients with PTSD excrete lower levels of cortisol than similarly-exposed trauma victims who do not develop PTSD. Further, recent research has shown that lower cortisol levels present soon after a trauma are associated with increased risk for developing PTSD symptoms. These results suggest that higher levels of cortisol during and immediately after a traumatic event may buffer the development of PTSD symptoms. In addition, preliminary findings have suggested that exogenously elevating patients' levels of cortisol during and immediately following trauma results in decreased incidence of PTSD. However, these data were collected on relatively small samples of trauma patients with confounding medical conditions (e.g., shock, cardiac surgery, or paralysis). A randomized controlled trial (RCT) is necessary to determine the efficacy of early cortisol administration at buffering the development of post-traumatic stress in a heterogeneous trauma sample.