The average free choline level was determined to be 14 mumol/L in peritoneal dialysates and 22 mumol/L in the plasma of 30 patients on continuous ambulatory peritoneal dialysis (CAPD). Daily choline loss via dialysate averaged 129 mumol with 32 mumol choline lost per dwell. Daily choline loss via the dialysate was positively correlated with plasma choline concentrations. Choline levels in dialysate during CAPD exceed plasma levels of choline 9 mumol/L in healthy individuals.