Haematological values of the eastern chipmunk (Tamias striatus) infected with Cuterebra emasculator were compared to those of non-infected hosts. Parasitized animals were anaemic and had a leucocyte count approximately twice that of the parasite-free animals. The differential leucocyte count varied with the stage of development of the parasite. Activity of the host was little affected by the presence of the warble during its parasitic invasion of the host tissue. Subsequent to the parasite leaving the host, the lesions became purulent; the activity of the host at this time was severely reduced.