Plasma tryptophan (Trp) concentration in its total (TTrp) and non-protein-bound free form (FTrp) and its metabolite 5-hydroxyindole-3-acetic acid (5-HIAA) as well as muscle Trp contents (MTrp) were studied in 12 uraemic patients undergoing continuous ambulatory peritoneal dialysis (CAPD), 10 renal