The plasma thyrotropin levels were determined in 35 children, aged 5 to 30 months, who were suffering from severe malnutrition due to socioeconomic factors. Plasma thyrotropin hormone was found to be normal in patients with the marasmic-kwashiorkor type of malnutrition (0.20 ± 0.07 mU/ml) and moderately decreased in those with the marasmic type (0.13 ± 0.04 mU/ml), despite the tendency to low levels of protein-bound iodine and thyroxine. Some patients also had abnormal amounts of the hormonally inactive precursors monoiodotyrosine and diiodotyrosine circulating in their plasma. These findings suggest that the reduced thyroid activity in infantile marasmus can be partly due to a decrease of anterior pituitary stimulation.