SUMMARYThe prevalence of nasal colonization and infection with methicillin-resistant Staphylococcus aureus (MRSA) among patients and staff was studied in a section of a Paediatric Surgical Unit in Lisbon between February and July 1985. Nasal colonization was demonstrated in 41 % of burned patients, 5 % of non-burned patients and 35 % of the nurses. Infection by MRSA occurred in 30 % of the burns.The isolates had identical serological patterns, slight differences on phage typing and were resistant to methicillin, cephalosporins, tetracycline, erythromycin and aminoglycosides. A chloramphenicol resistance plasmid of 3 Md was present in those isolates which were chloramphenicol resistant and a small plasmid of 1-7 Md which coded for constitutive erythromycin resistance was present in many isolates. Gentamicin, tetracycline and inducible erythromycin resistance were chromosomal.Several reasons for the apparent low virulence of the isolates are discussed.

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