The case reported represents an unusual mode of transmission of tularemia from cat to man, with fatal outcome. The use of the modified Dieterle spirochete stain demonstrated F tularensis in tissue when all other routine stains failed. Direct immunofluorescent staining confirmed the presence of the organism in tissue sections. F tularensis and the etiologic agent of Legionnaires' disease are similar only in their ability to stain with the modified Dieterle stain and their inability to stain with conventional histochemical technics.