Transfer of autologous haemoglobin from the peritoneal cavity was evaluated retrospectively in 14 patients who received this marker intraperitoneally (group 1) during routine continuous ambulatory peritoneal dialysis (CAPD). Five additional patients were studied during acute peritonitis (group 2). A model for balance of both dialysate volume and amount of haemoglobin is developed to assess movement of the compound into lymph or adjacent tissues. Under the conditions of the study the transfer was slow (8 +/- 10 ml/h) in patients without peritonitis (group 1), and significantly faster (25 +/- 22 ml/h) in those with peritonitis (group 2). These clearance values are the upper limits for lymph flow.