The complement-fixation test for endemic typhus has been shown to be specific by comparing the results obtained using serums from 15 cases of proved cases of endemic typhus and from 37 cases diagnosed clinically as typhus with those obtained using serums from cases of syphilis, leprosy, tuberculosis, rheumatic fever, malaria, undulant fever, tularaemia, trachoma and a few specimens from lymphopathia venereum.