Dialysate effluent protein content was measured in 22 patients undergoing continuous ambulatory peritoneal dialysis (9 with and 13 without previous peritonitis). The average amount of protein in those patients without peritonitis was 1.3 g/2 liters exchanged over a 6-hour period, while that of patients with previous peritonitis was 2.6 g/ 2 liters exchanged over the same period. 71 % of protein found in the dialysate of 2 patients was albumin. Despite the difference in the amount of protein lost between those without and those with peritonitis, there was no significant difference in their mean serum albumin levels (3.2 and 3.4 g%, respectively) which were only slightly below the normal range. The previously reported high protein losses in patients undergoing CAPD are probably the result of frequent episodes of peritonitis and a higher number (five) of daily exchanges.