Patient-to-patient transmission enables vancomycin- resistant enterococci (VRE) outbreaks. Outbreak management is expensive and time consuming, and therefore the possibility of VRE eradication is desirable. Since vancomycin is scarcely absorbed in the gastrointestinal tract, treatment with vancomycin per os may result in very high gastrointestinal concentrations (many times the minimum inhibiting concentration (MIC)). The purpose of this study is to measure in vivogastrointestinal concentrations of vancomycin in patients that are treated with a standard dose orally, and to investigate in vitro whether vancomycin is able to kill VRE at concentrations up to 2,000 times the MIC.