We have traced an episode of contamination of a fiberoptic bronchoscope with a Proteus species to an index patient. Bacterial cultures obtained by aspiration through the fiberoptic bronchoscope from 11 of 12 subsequent bronchoscopies in 8 additional patients grew a Proteus species with sensitivities similar to those of the initial isolate. Culture of the fiberoptic bronchoscopic specimen yielded an identical organism. There were no definitive ill effects in the patients. These findings necessitated a change in our fiberoptic bronchoscope disinfection protocol as well as development of culture surveillance mechanism to detect breaks in the cleaning procedure. The importance of this and avoiding potential outbreaks of fiberoptic bronchoscope-related infeciton is emphasized.