Comparison of bot-infested and bot-free chipmunks collected during 1966–1969 revealed no significant differences in rate of infestation among sex-age classes. Splenomegaly and thymic involution were associated with bot infestation, and adrenal weights were greater in bot-infested adult females. Parasitized animals of all sex-age classes tended to be larger than non-parasitized individuals, and reproductive organs were heavier in infested adults of both sexes. Evidence of bot-induced mortality was not found, but results indicate the possibility of differential loss of bot-infested animals from the population.