OBJECTIVE: To investigate and control an apparent outbreak of lower respiratory tract infections due to Aureobasidium species. DESIGN: Outbreak investigation. SETTING: University-affiliated medical center. PATIENTS: Nine patients who underwent bronchoscopy between June and August 1998. RESULTS: Ten bronchoalveolar lavage (BAL) fluid cultures from nine patients grew Aureobasidium species during the outbreak period; whereas, respiratory specimens from only two patients grew Aureobasidium species during the preceding 6 years. No patient was judged to have true infection due to Aureobasidium species either before or after bronchoscopy. Nine of the 10 bronchoscopies that yielded Aureobasidium species were performed in the outpatient bronchoscopy suite. The Aureobasidium isolates were not associated with any one bronchoscope. Observation of bronchoscopy procedure revealed that plastic stopcocks labeled for single use were reused on different patients during BAL. There was no record of how many times each stopcock was being reused. After each use, the stopcocks were placed in an automated disinfection machine designed for bronchoscopes. Culture of the stopcocks after they had been "disinfected" yielded a heavy growth of Aureobasidium species, while culture of fluid from the automated disinfection machine was negative. Reuse of the stopcocks was halted, and, during the following 6-month period, Aureobasidium species were not isolated from any BAL specimen. CONCLUSIONS: Reuse of medical equipment labeled for single use is potentially hazardous, especially if no quality control system is in place to monitor sterility and function after reprocessing.