We present the clinical results of a prospective protocol of the treatment of Staphylococcus aureus nasal carriers (SANCs) in our continuous ambulatory peritoneal dialysis unit with mupirocin (Bactroban, SmithKline Beecham Pharmaceuticals, Philadelphia, PA). We monitored the incidence of peritonitis and catheter exit-site infection, the rate of infection-related catheter loss, and the degree of association between SANC state and S aureus infection. The study group included 94 patients with a follow-up of 1,097 patient-months (phase B). The same information was retrospectively collected among 74 continuous ambulatory peritoneal dialysis patients treated during the 24 months preceding the study period (follow-up of 1,043 patient-months) (phase A). S aureus nasal carriage was observed in 47.5% of the patients. Mupirocin was very effective in eradicating S aureus from the nares, but most patients required periodic retreatment. The incidence of S aureus peritonitis decreased from 1 episode/58 patient-months in phase A to 1 episode/548 patient-months in phase B, and the incidence of exit-site infection decreased from one episode/55 patient-months in phase A to 1 episode/137 patient-months in phase B. However, there was a simultaneous increase in the incidence of infections by other gram-positive and -negative bacteria. The rate of catheter loss after peritonitis (P = not significant) or exit-site infection (P < 0.05) tended to decrease from phase A to phase B. Seventy-seven percent of the peritonitis infections and 74% of the exit-site infections by S aureus occurred in SANCs.(ABSTRACT TRUNCATED AT 250 WORDS)