Peritoneal effluent of patients on chronic ambulatory peritoneal dialysis (CAPD) contains a surface-active material (SAM) made up of phospholipids and showing phosphatidylcholine on thin-layer chromatography. This substance drastically lowers surface tension, helps to repel water and has a lubricating effect. The presence of stratified phosphatidylcholine on the peritoneum might narrow the stagnant dialysate fluid layer and situations which can alter the quantity or composition of SAM may affect peritoneal transport and also, perhaps, the formation of adherences. This led us to verify, experimentally, the presence of phospholipids in basal conditions, after CAPD and during peritonitis and to check if addition of phosphatidylcholine to dialysis liquid is able to modify water transport in patients with low ultrafiltration and peritonitis. Phospholipids in the dialysis effluent of patients who have been on CAPD for a long time are lower than observed in the first days of peritoneal dialysis. A more drastic, significant decrease in phospholipids was observed in patients with low ultrafiltration and in patients with peritonitis. Mean ultrafiltration significantly increases in patients with low ultrafiltration and in those with peritonitis during dialysis exchanges containing phosphatidylcholine (50 mg/l) indicating that the latter is able to restore normal physiological conditions.