Plasma carnitine, amino acids and lipids levels were studied in ten uraemic children treated with haemodialysis and given amino acid supplementation with and without carnitine. As carnitine is synthesised from lysine and methionine and has a significant influence on lipid metabolism, the relationship between these was examined. Amino acid supplementation (0.25 g/kg body weight) was started with the intention of improving the plasma amino acid pattern in these children and increasing the concentration of lysine, which is the substrate for carnitine synthesis. Amino acids were administered i.v. during dialysis and carnitine (25 mg/kg body weight i.v.) was administered after dialysis three times a week. Concentrations of most essential amino acids were decreased in these patients. The first period of amino acid supplementation did not increase plasma levels of the essential amino acids, with the exception of tyrosine (P < 0.01). After the second period of supplementation, methionine was increased (P < 0.01), isoleucine was decreased (P < 0.01), but tyrosine normalised and was significantly lower than after the first period (P < 0.05). Thus overall amino acid supplementation did not improve amino acid levels; it was inconsistently associated with a further decrease in high-density lipoprotein-cholesterol and an increase in total protein levels. Lysine concentrations after amino acid supplementation remained low. Paradoxically, before carnitine supplementation a positive correlation between free carnitine and triglycerides was observed.(ABSTRACT TRUNCATED AT 250 WORDS)