Eradication of methicillin-resistant Staphylococcus aureus (MRSA) carried by inpatients or healthy hospital personnel by topical use of antibiotics is an important step for preventing outbreak of MRSA nosocomial infection. In the screening of the antibiotic best suited for this purpose, we have found that polymyxin B, a commonly used antibiotic for gram-negative infection, had an unexpected strong cytokilling activity towards MRSA clinical strains, which was more potent than that of vancomycin or gentamicin. The data suggested that polymyxin B could be an antibiotic of choice in the treatment of topical carriage of or infection caused by MRSA.