The evolution of the aluminum (A1) serum levels during a 2-year follow-up and the peritoneal transfer of A1 were studied in 22 patients treated by continuous ambulatory peritoneal dialysis (CAPD), using a dialysate with a very low A1 concentration (r = 0.25 - 0.30 mumoles/liter). Patients were divided in three groups. A transfer of A1 from the patient to the dialysate was observed in all patients. In group 1, patients exclusively treated by CAPD and who have never received aluminum-containing phosphate binders (ACPB), mean level (+/- SD) of serum A1 stabilized within a safe range (0.60 +/- 0.28 mumoles/liter). In group 2 the oral administration of ACPB in patients exclusively treated by CAPD induced a slow and progressive increase of A1 serum concentration despite the increase of the A1 excretion through the peritoneal route. In group 3, patients previously treated by hemodialysis and receiving ACPB, the high serum A1 levels observed before treatment by CAPD decreased rapidly on CAPD. A1 removal through the peritoneum was higher in group 3 than in group 2 despite serum A1 levels not statistically different in both groups. A1 removal through the peritoneum is mainly influenced by serum and dialysate A1 concentration. A1 body stores could play a role in the transfer of A1 through the peritoneum. Three cases of A1 poisoning due to the accidental use of a dialysate with a high A1 content are reported.