The aim of this study was to evaluate the activity of a dry mist-generated hydrogen peroxide (DMHP) system (Sterinis; Gloster Sante Europe, Labege cedex, France) against methicillin-resistant Staphylococcus aureus (MRSA) and Acinetobacter baumannii. McFarland 0.5 suspensions of 2 test bacteria, either pure or containing 5% sterile serum, were prepared and inoculated onto sterile stainless steel disks. Each disk in a Petri dish-with the Petri dish cover either closed or open-was placed in different locations in an intensive care unit room. Quantitative cultures were performed after the cycle. No growth occurred on the disks in the absence of a barrier, except 1 disk containing serum. Existence of a barrier, as a drawer or a covered Petri dish, caused failure in the disinfection activity. The mean reduction in initial log(10) bacterial count was lower for both of the test bacteria in presence of a barrier: 4.44- to 4.70-log(10) colony-forming units (cfu) decrease was observed in absence of a barrier, whereas 1.49- to 3.79-log(10) cfu decrease was observed in presence of a barrier. When the culture results were compared according to organic load content, the mean (±standard deviation) reduction of initial contamination in pure and in serum containing MRSA suspensions was 4.25 ± 1.20- and 3.34 ± 1.89-log(10) cfu, respectively. The mean (±standard deviation) reduction in pure and in serum containing A baumannii suspensions was 4.34 ± 0.89- and 3.87 ± 1.26-log(10) cfu, respectively. The differences were statistically significant (P < .001). Sterinis was capable of killing MRSA and A baumannii on open surfaces; however, it was not effective in closed or semiclosed areas. Presence of serum also caused failure in the disinfection activity of the system. Copyright © 2011 Association for Professionals in Infection Control and Epidemiology, Inc. Published by Mosby, Inc. All rights reserved.