Heteroresistant vancomycin-intermediate sensitive staph aureus (hetero-VISA, hVISA, hGISA) isolates are those in which the prevalent colonies are vancomycin susceptible but in which some of the isolates demonstrate phenotypes which are intermediate or resistant to vancomycin9. Hetero-VISA has been proposed as an etiology for vancomycin treatment failure in some patients. These hetero-VISA isolates may exhibit vancomycin-susceptibility when analyzed by automated testing because automated systems are incapable of identifying rare hetero-VISA colony forming units (CFU's) within single large inoculums10. Without plating and more detailed testing, the true incidence of hetero-VISA isolates may be underestimated. No large direct comparison of automated and non-automated MRSA isolate sensitivities to vancomycin has been reported. This investigation seeks to determine the prevalence of hetero-VISA in sputum isolates of MRSA in a major tertiary referral center and define the sensitivity of automated testing.