This study was undertaken to evaluate the effectiveness of prophylactic intranasal mupirocin for peritonitis in patients on continuous ambulatory peritoneal dialysis (CAPD). A total of 49 patients undergoing CAPD for at least 6 mo were followed for 1 year. A nasal smear was obtained from each patient at the beginning and end of the study. Intranasal mupirocin ointment was administered to the nares twice daily for 5 d every 4 wk in the mupirocin group. The frequency of Staphylococcus aureus nasal carriage was similar in both groups at the beginning, and S aureus was eradicated in 56.5% of patients in the mupirocin group; 29% of patients in the control group had negative nasal smear culture findings atthe end of the study. Peritonitis episodes occurred at rates of 4.3% in the mupirocin group and 4.1% in the control group (P > .05). Prophylactic administration of intranasal mupirocin ointment was ineffective in reducing episodes of peritonitis.