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The introduction of antimicrobial surfaces into healthcare environments is believed to impact positively on the rate of healthcare-associated infections by significantly decreasing pathogen presence on surfaces. We report on a novel efficacy test that uses a dry bacterial inoculum to measure the microbicidal efficacy of antimicrobial surfaces. An aerosolised dry inoculum of S. aureus or A. baumannii was deposited on copper alloy surfaces or a hospitalgrade stainless steel surface. Surviving bacteria were enumerated following incubation of the inoculated surfaces at an environmentally relevant temperature and relative humidity (RH).Damage caused to bacteria by the aerosolization process and by the different surfaces was investigated. Dry inoculum testing showed a <2 log10 reduction in S. aureus or A. baumannii on the copper alloy surfaces tested after 24 h at 20°C and 40% RH. Potential mechanisms of action coper included membrane damage, DNA damage and arrested cellular respiration.The aerosolization process caused some damage to bacterial cells. Once this effect was taken into account, the antimicrobial activity of copper surfaces was evident. Our test provides a realistic deposition of a bacterial inoculum to a surface and as such a realistic protocol to assess the efficacy of dry antimicrobial environmental surfaces in vitro.