Immune function declines significantly with advancing age. While many components of the immune system are adversely affected, T cell-dependent functions are most dramatically compromised. This is most likely a result of involution of the thymus gland known to occur with age. Defects in T cell proliferative capacity/responsiveness, interleukin-2 production and receptor expression, signal transduction, and cytotoxicity are frequently cited problems associated with immunosenescence. The stress imposed by a single bout of exercise elicits a number of cardiovascular, thermoregulatory, and neuroendocrine responses that can directly influence many variables associated with the immune system. Consequently, during exercise, as well as into the subsequent recovery period, immune function can be significantly altered. Further, recent work has shown that as a result of endurance training adaptations in both baseline and exercising immune function can occur. However, extremely little is known regarding the interaction between exercise, aging and the immune system. Given that a number of age-related changes occur in many systems (e.g., neuroendocrine) known to alter immune function both at rest and during exercise, it would be of value to learn the extent to which both acute and chronic exercise influence immune function in the elderly.