The serum carnitine (total carnitine), total protein, amino acid, and triglyceride levels were determined in children on continuous ambulatory peritoneal dialysis (CAPD). Compared with levels in controls, serum carnitine levels were significantly decreased in patients on CAPD for more than 4 months, while those of patients on CAPD for 1–3 months were not decreased. Patients on CAPD for more than 4 months also showed lower serum total protein levels than in normal controls. The mean triglyceride levels in patients on CAPD for both 1–3 months and more than 4 months were higher than those in normal controls. Among the amino acids, the serum levels of tryptophan, isoleucine, leucine, tyrosine, valine, serine, and aspargine were significantly lower in patients treated with CAPD than in normal controls, whereas the levels of other amino acids were either increased or not changed. Isoleucine and leucine levels showed a strong correlation with serum carnitine. Our data suggest that malnutrition plays a role in the decrease of serum carnitine levels in patients receiving CAPD.