Phospholipid molecular species have been determined in the spent dialysates of 21 patients on continuous ambulatory peritoneal dialysis (CAPD) by LC-ESI-MS.Glycerophosphoehtanolamine (PE), phosphatidylinositol (PI), phosphatidylcholine (PC), sphingomyelin (SM) and lyso-phosphatidylcholine (LPC) were found (Fig.1), and 31 molecular species were identified and determined in the spent dialysate.The main phospholipid class is PC (70% of total phospholipids) in which the predominant molecular species are PC 16∶0/18∶2 (27.5 % of PC), PC 18∶1/18∶1 plus PC 18∶0/18∶2 (19.1% of PC) and PC 16∶0/18∶1(16.1% of PC).These findings might provide more clues or suggestions for the surfactant replenishment in the peritoneal dialysis.