Zinc-deficient animals and children have thymic atrophy and an increased susceptibility to infections. Children with protein-energy malnutrition similarly have thymic atrophy, zinc deficiency, and increased susceptibility to infections. 8 children, recently malnourished, who were supplemented with zinc, showed an increase in thymic size as judged radiographically. It is suggested that zinc deficiency may play a part in the thymic atrophy and infections associated with malnutrition.