The authors studied seven automatic washer disinfectors for flexible endoscopes with two methods. The first method, a microdilution method, studied the bactericidal activity of the seven disinfectants against 21 strains: four reference strains, 14 hospital strains reported in the literature as nosocomial strains responsible for infections transmitted by flexible endoscopes and three vancomycin-resistant Enterococci. The ability of the seven automatic washer disinfectors to decontaminate flexible endoscopes following inoculation with four reference strains was studied with the second method. There were three kinds of results: the results of three automatic washer disinfectors in conformity with both methods; the results of three automatic washer disinfectors conformity with 1 method only; the results of one automatic washer disinfector without conformity with any methods. Both methods should be used for evaluation of automatic washer disinfector. Then, these results emphasize the necessity to modify the use of disinfectants and/or the systems of some automatic washer disinfectors.