Insulin-like growth factor-1 (Igf1), a useful and early marker of undernutrition in inflammatory diseases, is dependent on the calorie and protein content of the diet. In 31 children and adolescents with cystic fibrosis (CF), a chronic inflammatory disease, the influence of the degree of liver dysfunction and the protein and calorie content of the diet on the circulating Igf1 was evaluated. No significant difference in the median plasma Igf1 concentration, measured by RIA, between the CF children (0.80 U/ml) and a for age and puberty matched control group (0.61 U/ml) was found. Expressing the Igf1 concentration as a percentage of normal for age, gave for the CF patients with liver involvement a lower level (median: 76%) than in those without (median: 101%). No correlation existed between the circulating Igf1 levels and the body height SDS, the body weight index and the calorie or protein intake of the patients