Our previous studies demonstrated that, over single peritoneal dialysis cycles, amino acid-based dialysis solutions (AAD) were effective in dialyzing children with chronic renal failure (CRF) and offered metabolic advantages over traditional glucose dialysis solutions. The AAD, however, resulted in undesirable elevations of certain plasma amino acids, notably methionine. To further investigate the relationship between dialysate and plasma amino acid levels, we assessed the plasma amino acid response to a new AAD with relatively low methionine content (Vamin-based) over separate 5-h cycles with 1.3 and 2.3% AAD in eight patients with CRF (age 1-9 years) on continuous ambulatory peritoneal dialysis (CAPD). There was a net absorption of 70-73% of the amino acids, the net absorption of individual amino acids corresponding with the AAD composition. Plasma amino acid levels rose with AAD, peaking by 1 h postinfusion. Although most amino acids fell to preinfusion levels at the end of the cycle (including methionine), isoleucine with the 1.3% AAD and isoleucine, leucine, phenylalanine, and tyrosine with the 2.3% AAD remained significantly elevated. Having demonstrated in children that amino acids are absorbed from the peritoneal cavity in proportion to the AAD profile, modification of the current AAD is suggested.