Five patients were infected with a nontyphosal Salmonella species, Salmonella oslo. Three of the five patients had undergone endoscopy. Three possibilities existed to account for this outbreak: the positive cultures represented isolated events; there was one isolated event and a common source; or, all events were due to a common source. The results of our investigation were inconclusive, but suggested that the endoscope could have been responsible for some of the cases. Appropriate methods for sterilizing endoscopes are reviewed, including sterilization with 2.5 per cent glutaraldehyde solution and ethylene oxide gas. The organism was unusual in its resistance to chloramphenicol and ampicillin; however, it was sensitive to a sulfonamide and trimethoprim. Two patients became culture-negative for S. oslo on treatment with this combination.