Long-term intravenous supplementation with low dose L-carnitine (5 mg/kg body wt) was investigated in seven hemodialyzed children with type IV hyperlipoproteinemia. Carnitine was given at the completion of each hemodialysis treatment (3 times a week) over a period of five months. This treatment resulted in a rise in total plasma carnitine concentrations (117.7 +/- 33.0 microM) as compared to before therapy (37.9 +/- 15.8 microM); the free fraction was the chief portion of this elevation. Prior to therapy the patients had high plasma triglyceride concentrations (3.82 +/- 1.6 mM) which were markedly reduced after five months of carnitine therapy (1.86 +/- 0.7 mM; P less than or equal to 0.05). The initially low HDL-cholesterol levels (0.91 +/- 0.2 mM) were increased (1.13 +/- 0.2 mM; P less than or equal to 0.05) after supplementation. Thus, long-term low-dose carnitine supplementation improves the disturbed lipid metabolism; this suggests an important role for carnitine in uremic children and may justify the use of supplemental carnitine.