During a hospital outbreak of methicillin-resistant Staphylococcus aureus (MRSA), involving more than 200 patients, 40 patients and 32 hospital staff who were stable nasal carriers of MRSA received topical application of 2% mupirocin, formulated in a white soft paraffin and lanolin ointment, to their anterior nares for five days. Nasal carriage was eliminated in all patients and staff, usually within the first 48 h of treatment. Of the 40 patients, 36 remained clear of nasal MRSA for the duration of their follow-up (mean = 2 weeks) and four became re-colonized one to five weeks after their course. Immediately after the course, the number of patients with MRSA isolated from wounds and wrists fell from 16 to 7, and from 16 to 3, respectively. Of the 32 staff, all were negative one week after the course, and of the 22 still available for follow-up at eight weeks, all were consistently negative (mean period of follow-up = 7.8, range = 1-20 weeks). Four patients and five staff were re-colonized with MRSA between one to five, and two to twelve weeks, respectively, after treatment. Overall, in the post-treatment follow-up, 98.6% of the staff-weeks and 90.1% of the patient-weeks were free of nasal MRSA. MICs of mupirocin for both pre and post treatment isolates were all 0.03 or 0.06 mg/l. The elimination of nasal MRSA by mupirocin, and the introduction of isolation facilities, were associated with the control of the outbreak.