Albumin and protein removal rates were studied in 18 patients undergoing continuous ambulatory peritoneal dialysis (CAPD). In nine patients simultaneous studies of albumin distribution and turnover were performed. Total albumin loss was 4.23 +/- 1.42 g/1.73 m2/24 hr; total protein removed was 8.79 +/- 4.21 g/1.73 m2/24 hr. Although these values were well within the range for severe nephrosis, serum albumin concentration remained nearly normal, 3.7 +/- 0.5 g/dl. Plasma albumin mass, 120.0 +/- 25.2 g/1.73 m2, and total albumin mass, 249 +/- 29.1 g/1.73 m2, did not differ from those of the control group. Compared with the control group, patients had reduced albumin catabolism, 9.76 +/- 1.74 g/1.73 m2/24 hr versus 13.8 +/- 0.77 g/1.73 m2/24 hr (P less than 0.001). Within the patient group albumin synthesis increased with increased albumin loss. Serum albumin concentration correlated negatively with albumin losses (P less than 0.001). The CAPD patients maintained albumin homeostasis through decreased albumin catabolism and increased synthesis. All major albumin pools were maintained despite massive albumin loss.