A child with hypogammaglobulinemia and intractable diarrhea underwent parenteral alimentation for five months. A clinical syndrome of acrodermatitis enteropathica subsequently developed associated with a depression in thymus-dependent lymphocyte (T cell) numbers, abnormal T-cell mitogen-induced blast transformation, and anergy to skin test antigens. Plasma zinc levels were found to be abnormally low. Zinc therapy resulted in dramatic resolution of the clinical manifestations of acrodermatitis enteropathica. Cell-mediated immune function was also restored to normal, suggesting an important role for zinc and possibly other trace metals in cellular immune responses.