The emergence of methicillin-resistant Staphylococcus aureus (MRSA) in a critical care facility creates a multifaceted epidemiological problem in uncovering the source of infection. This study was undertaken to determine the true etiology of MRSA burn wound infections. Patients with a 30% or greater TBSA burn had both burned and unburned skin surface cultured upon admission, using RODAC plates. All other body fluids were cultured when sepsis was suspected. Admission cultures of 14 patients who developed MRSA wound infections were examined for methicillin-resistant organisms. Both admission isolates and infection isolates were compared by antibiogram analysis. Of the 14 patients admitted who developed MRSA infections, 57.1% of these had methicillin-resistant staphylococci present on admission. However, the remaining 42.9% of the patients had methicillin-sensitive, B-lactamase positive staphylococci present on admission. Isolates of group D streptococci resistant to methicillin were isolated in 35.7% of the patients. This data suggests that burn wound infections caused by MRSA very likely arise from the endogenous flora present at the time of injury through conferring the resistant plasmid by conjugational transfer.