The role of emotional factors in the growth failure of the deprivation syndrome was investigated by measuring adrenocortical and thyroid functions; three control groups had growth failure from other causes. Cortisol secretion rate was elevated in 50% of cases, but not in controls. Excessive appetites and a significantly higher weight gain per unit of nitrogen retention during ad libitum feeding were evidence of increased biological activity. Plasma cortisol was higher on admission than after weight gain; standard deviations decreased with recovery, suggesting establishment of a diurnal rhythm. Serum thyroxine (T4) was decreased in patients with the deprivation syndrome and in controls with growth failure due to undernutrition, but the basal metabolic rate was normal. The low T4 thus seems to reflect a decrease in thyroxine binding proteins, apparently on the basis of undernutrition.