One of the most compelling, yet challenging, as pects of immunology is to understand the mechanisms by which individual parts integrate into a functiona whole. Limited studies have addressed this impor issue. Corticosteroids, which are released during cold stress, hypothermia, or both, have a well When documented immunosuppressive effect cold stress is applied to an animal, specific changes n the cellular components can be observed Sundaresan and colleagues' showed that when a bino rats were subacutely stressed with cold water immersion, the total number of immune cells was initially expanded. Total white cell count was in creased, as were total numbers of eosinophils and basophils. Phagocytic and avidity indices were also increased in phagocytic cells. However, Cheng and showed that prolonged cold water colleagues stress actually has an immunosuppressive effect they reported a decreased number of thymocytes and splenocytes, as well as diminished blastogen esis of T cells and lowered activity of natural killer cells. Macrophages were found to be less responsive to interferon gamma, and because these antigen presenting cells are crucial for initiating immune cascades, the impairment of macrophage function could be a significant cause of a dampened immune esponse. While the mice in the Cheng experiment were obviously also stressed by anxiety and exer cise, these results have implications for many set- tings of human accidental hypothermia