Since the first attempts (1) to eradicate nasal carriage of Staphylococcus aureus with local applications of penicillin, many other topical and systemic antimicrobial agents have been tested, all with limited success. More recently, mupirocin has been much more successful and, in a controlled trial, nasal carriage of S. aureus was eliminated in all subjects and when re-colonisation eventually took place, only 29% had relapsed with their pre-treatment strain. During an MRSA outbreak at a London hospital, standard infection control measures failed to prevent colonisation and infection of more than two hundred patients, but the use of mupirocin was associated with epidemiological control. Of forty patients and thirty-two staff studied, 98.6% of staff and 90.1% of patient-weeks were free of nasal MRSA after treatment. Although resistance to at least 40 mg/l of mupirocin can be produced in vitro and resistant S. aureus have been isolated from patients undergoing prolonged skin treatment with mupirocin, there has been no evidence for the emergence of mupirocin resistance as a mechanism for the relapse of nasal carriage.