This is a research project with three specific aims. Using a murine model, the first aim is to study the relationship between cytokine levels in serum, spleen and brain and the development of fatigue.The second is to attempt to determine whether the administration of neutralizing antibodies specific to cytokines blocks the development of fatigue. Lastly, the author will evaluate the modulating effects of age, sex and genetics on the development and severity of chronic fatigue. Two objective measures will be used to quantify fatigue: loss of daily running activity on an exercise wheel and time elapsed before resumption of grooming behavior after swimming (exercise-induced fatigue). Corynebacterium parvum antigen will be used to stimulate the immune system in BALB/c mice. Cytokine levels in serum will be correlated with development of fatigue. Antibodies specific to these cytokines will be used to determine the involvement of cytokines in inducing fatigue. The influence of age, sex and genetic factors on the degree and duration of fatigue will be explored.