The transmission of infectious agents following endoscopy has been demonstrated in several studies. Most endoscopy-related infections were caused by bacterial agents and, less frequently, by viruses (hepatitis B and C). Published studies report isolated cases of nosocomial infections following endoscopy, but the practical aspects of the investigation are rarely described. The objective of this article is to report on and discuss the investigation conducted following a malfunction of an endoscope washer-disinfector (LDE) in a gastrointestinal endoscopy unit. (R.A.)