The three cases we have presented implicate F meningosepticum as a significant pathogen causing disease in immunocompromised adult patients. Since this organism is of low pathogenicity but may be found in the hospital environment, its identification as a pathogen raises the suspicion of a nosocomial source of infection, and a search for the source should be made. Furthermore, with regard to the choice of antimicrobial therapy, it must be remembered that this organism is resistant to most antibiotics commonly used to treat gram-negative bacilli, and disk diffusion technics may not reliably predict actual antibiotic sensitivity.