Aluminium concentration was determined in dialysates used for HD and for PD and in the serum of normal subjects and of uraemic patients on treatment with HD and with PD. The main finding of this study was that serum A1 levels are significantly higher in patients on PD than in patients on HD. We conclude that the use of dialysates with pH less than 5.5 could contribute to a positive balance of A1 during PD.