1751 Ageing has been associated with a decline in several aspects of the immune system. Moderate exercise may restore immune function in aged mice and reduce susceptibility to respiratory infection. PURPOSE: We studied the effects of moderate exercise training on susceptibility to infection in aged mice using our mouse model of respiratory infection (Davis et.al. J. Appl. Physiol Physiol. 83 (5): 1461–6 1997). Viral titers and inflammatory cytokine responses in the lung were also determined. METHODS: Female CD-1 mice were randomly assigned to one of three groups (n = 14–18/group). Exercise aged mice (EX-aged) (18 months old) ran on a treadmill for 45 min/day, 6 days a week for 6 weeks at 18m/min, 5% grade. Control aged mice (CON-aged) (18 months old) and control adult mice (CON-adult) (5 months old) remained in their cages during this time. Following the last day of training or rest, mice were intranasally inoculated with Herpes Simplex Virus-1 (HSV-1). They were monitored twice daily for morbidity and mortality as well as symptom severity for 21 days. Additional mice (n = 10/per group) were inoculated with HSV-1 and sacrificed on day 4 following infection. Lungs were analyzed for viral titers and inflammatory cytokine responses. RESULTS: Ageing was associated with a significant increase in morbidity (47%, P = 0.0015), mortality (45%, P = 0.007) and symptom severity score on days 5 through 11 post-infection (P<0.05). Exercise reduced the increase in morbidity (23%, P = 0.009) and symptom severity score on days 5, 7 and 8 post-infection (P<0.05). There was no difference in mortality. Ageing resulted in a trend toward an increase in lung viral titers (P = 0.1) with an associated increase in IL-1β (P<0.001). Exercise reduced this increase in lung viral titers (P = 0.07) and IL-1β (P = 0.003). CONCLUSION: These data suggest that moderate exercise training can help restore some of the negative effects of ageing on immune function and therefore reduce susceptibility to infection in mice. Funded by a grant from the American College of Sports Medicine