Serum carnitine levels were investigated in a group of normal adults and two groups of patients with active schistosomiasis who also showed signs of malnutrition and vitamin deficiency. The first group consisted of 16 patients with Schistosoma mansoni and/or Schistosoma haematobium infection. They received an adequate diet supplemented with vitamin and iron therapy and received no treatment for their parasitic infection till their hemoglobin levels were restored to normal. The second group consisted of 12 patients with schistosomiasis as well as intestinal polyposis. They received the same diet as the first group but because of their poor condition were immediately treated for parasitic infection. Results showed that both groups of patients had subnormal levels of serum carnitine with the polyps patients (Group II) having a significantly lower level than patients with simple schistosomiasis (Group I). After nutritional repletion a significant increase was observed in the carnitine levels of most patients in group I indicating a relationship between the nutritional status of the patients and their serum camitine levels. The patients with polyps also showed considerably increased camitine levels after treatment and dietary repletion. The usefulness of serum camitine measurement as an index of protein malnutrition in man is discussed.