Serum albumin level is a predictor of mortality and morbidity for continuous ambulatory peritoneal dialysis (CAPD) patients; however, few studies have analyzed SA and dialysate albumin loss in automatic peritoneal dialysis (APD) patients. The proposal of this study have been measures the dialyzate albumin loss in APD patients, total and separately day and night, its relation with peritoneal permeability and serum albumin levels. Also we have compared the dialysate and serum albumin with CAPD patients. We have studied 19 patients in APD (mean 51 +/- 14 years old, 6 females, 13 males) and 16 patients in CAPD (mean 57 +/- 16 years old, 9 females, 6 males). In all patients we performed PET, and their peritoneal effluent (24 h, day, night and 4 hours TEP), urine/24 h and serum were analyzed for: albumin, glucose, creatinine and urea. We calculated, nPCR, ClCr/week and KT/V/week and normalized to 1,73 m(2), total (renal and peritoneal) and peritoneal. Dialysate and serum albumin concentrations were always determined by nephelometry. Results: In APD patients the albumin loss in the day-dialysate were found to be: 1.8 +/- 0.8 g; albumin loss night-dialysate 2.7 +/- 1.4 g; albumin loss/24 h: 4.2 +/- 2.0 g. In CAPD patients: albumin loss/24 h: 4.1 +/- 1.2 g (APD vs CAPD p = 0.7); serum albumin APD patients: 3.6 +/- 0.5 g/dl; serum albumin CAPD patients: 3.4 +/- 0.8 g/dl (APD vs CAPD p = 0.4). In APD patients the albumin loss/24 h was correlationed with D/P Cr 2 (p = 0.04, r = 0.48), KTV/week total (p = 0.03/r = 0.50) y ClCr/week peritoneal (p = 0.03, r = 0.49), but was not correlationed with serum albumin levels. Serum albumin levels was correlationed with age (p = 0.02, r = -0.60), nPCR (p = 0.02, r = 0.64), ClCr/week total (p = 0.02, r = 0.53) and CIU/week total (p = 0.04, r = 0.55). When we regarded dialysate albumin loss in 4 hours TEP-drainage in all 35 patients (APD and CAPD all together), we found significative correlation with D/P U2 (p = 0.001, r = 0.53), D/P Cr2 (p = 0.02, r = 0.47), D/P U4 (p = 0.04, r = 0.43), D/P Cr4 (p = 0.001, r = 0.56). Serum albumin levels was correlationed with D/P U2 (p = 0.04, r = -0.41), D/P Cr2 (p = 0.001, r -0.56), D/P Cr4 (p = 0.001, r = -0.43), G4/G0 (p = 0.02, r = 0.43). We don't found correlation of albumin serum levels with dialyzate albumin loss in 4 hours TEP. We conclude that the peritoneal albumin loss is similar in APD and CAPD patients. It's dependent, like on other peritoneal dialysis modalities, on peritoneal permeability. Serum albumin levels in our APD and CAPD patients is independent on albumin dialysate loss but dependent on protein intake and dialysis doses.