Staphylococcus aureus nasal carriage status (SANCS) has been recognized as a risk factor for patients on CAPD, due to a higher probability of suffering peritoneal catheter infections. The use of subcutaneous drugs (insulin dependent diabetics, drug addicts, HD patients and antiallergic vaccines), has been associated with increased risk of SANCS. On CAPD, erythropoietin (EPO) is almost universally used by the subcutaneous route. The objective of this paper was to evaluate the incidence and prevalence of SANCS in 85 CAPD patients by means of nasal smear and the influence of SANCS on peritoneal and catheter infection rate. Patients were divided in four groups according to diabetic status and EPO treatment (mean dose 2000 u. twice a week). The prevalence of SANCS in control groups was 30% in non-diabetics and 23% in diabetics. EPO treated patients showed a prevalence of SANCS of 39% in non-diabetics and 45% in diabetics due to the presence of 7 and 5 carrier patients respectively. SANCS patients (29% of the population), suffered 45% of peritonitis and 42% of exit-site infections caused by S. aureus. In a prospective part of the study, there was no difference in the frequency of developing positive cultures among EPO and control (30% of patients). No male EPO treated patients developed SANCS. We conclude that it is necessary to monitor S. aureus nasal carrier status periodically in CAPD patients especially in women. Whether or not subcutaneous erythropoietin treatment is implicated pathogenetically with SANCS, is not clarified by our data because of the frequent spontaneous appearance of SANCS among CAPD patients.(ABSTRACT TRUNCATED AT 250 WORDS)