Adult male rats were subcutaneously injected with dexamethasone at a dose of 1mg/kg B.w. for five doses. Another group of adult male rats were subjected to elevated ambient temperature and relative humidity for two and four days. The obtained results indicated that the dexamethasone treated group exhibited elevations in plasma levels of dexamethasone and decreased plasma levels of corticosterone. Interleukin-2 (IL-2) as well as peripheral blood lymphocyte transformation showed significant decreases than control group. Elevated ambient temperature and relative humidity for two and four days resulted in a significant elevation in the plasma corticosterone, while both IL-2 and the percent of responding lymphocytes to transformation was significantly decreased. It could be concluded that the stress response in adult male rats involves a series of events including impairment of immune function suggesting that interleukins may play an important role in this phenomenon.