THE BACTERIAL flora of the normal nasopharynx may be altered significantly during the therapeutic administration of sulfadiazine,1penicillin2or streptomycin.3Usually these changes are specific and selective, so that species of organisms which are highly susceptible to the drug are eliminated rapidly. More resistant groups of bacteria, which may be present in small numbers before therapy or may enter after therapy is begun, then multiply and become the predominant organisms during the first week of treatment. If these relatively drug-fast organisms are pathogenic, they may initiate a new bacterial infection in the patient during the course of treatment for the primary disease.4Furthermore, these strains may be transmitted to others, causing infections that require different antibacterial drugs for treatment.5 Studies of the effect of aureomycin on the normal flora of the body have been limited to the micro-organisms in the gastrointestinal6and genital tracts.7Collins, Gocke and Finland,8