Somatomedin C (Sm-C) is supposed to be a sensitive marker of malnutrition. Its relationship to growth and protein intake was investigated in 47 Moroccan children. The children (mean age: 7.5 +/- 2 yr) had no endocrine abnormality. Anthropometric parameters were measured, together with blood levels of Sm-C and growth hormone (GH). Lower values of Sm-C were found in the following situations: (a) growth retardation (more than -2 Sd, N = 23; Sm-C = 3.61 +/- 0.42 nmol/l vs. 13.38 +/- 1.52, P less than 0.02); (b) body weight less than 80% of expected weight for height (N = 8; Sm-C = 4.84 +/- 0.97 vs. 10.33 +/- 1.19, P less than 0.02); (c) boys with meat consumption less than 3 times per wk (N = 15; Sm-C = 4.03 +/- 0.71 vs. 12.35 +/- 2.01, P less than 0.002). Thus, lower values of Sm-C are found in association with weight insufficiency and lower protein intake. As has previously been assumed, serum Sm-C, which is regulated by nutrition, may be a sensitive tool in the assessment of nutritional status in developing countries such as Morocco. Furthermore, it could explain some cases of growth retardation in states of malnutrition.