PET is the most common test used to evaluate and classify the peritoneal membrane function while doing peritoneal dialysis. Patients and methods: This was a prospective and cass-series study, in which PET was used to evalulate and classify the peritoneal membrane function of patients with ESRD treated by CAPD at the Nephrology-Urology Department, Hospital Popular 115, from January, 2005 to January, 2007.