When combined with clinical cure data above, this in vitro evidence strongly questions the prudence of using vancomycin as the empiric antimicrobial agent in patients known to be at risk for MRSA, who may be critically ill with VAP and for whom a wealth of studies establish that failure to adequately treat empirically increases mortality. Determining the prevalence of MRSA isolates with marginal susceptibility to vancomycin or heteroresistance is the primary aim of this investigation. An accurate measure of MIC reproducibility between techniques and the current prevalence of MIC's which are only marginally susceptible will allow our institution and the medical community to determine the most appropriate role for vancomycin in the empiric antimicrobial regimen for patients thought to have VAP who are at risk for MRSA.