Permanent loss of the ultrafiltration (UF) capacity of the peritoneum has been observed with an increasing frequency among our patients treated by long-term intermittent (IPD) and/or continuous ambulatory peritoneal dialysis (CAPD).The analysis of various characteristics of our PD population (patients age, dialysis techniques, peritoneal infection rate and treatment duration) indicates that the incidence of this complication increases exponentially with the duration of PD, the loss of UF capacity being observed after a shorter period in CAPD than in IPD. These observations suggest that long-term irrigation of the peritoneal cavity leads to a progressive deterioration of the peritoneum resulting in its altered permeability with loss of the ability to ultrafiltrate; the cause of this abnormality is as yet unknown.