In a previously healthy 13-year-old girl with disseminated blastomycosis, immunodeficiency was considered because of lymphopenia and the slow response of her lung disease to therapy with amphotericin B. Cellular immunity was found to be profoundly impaired, with absent delayed cutaneous hypersensitivity to several common antigens, a decreased count of thymus-dependent lymphocytes in the peripheral blood and a greatly diminished in-vitro proliferative response of lymphocytes to phytohemagglutinin (PHA). Humoral immunity was intact. Two additional types of therapy were assessed: subcutaneous injection of transfer factor was associated with an unsustained increase in lymphocyte counts and a positive cutaneous response to PHA but no clinical change; parenteral alimentation to ensure an adequate energy intake was associated with rapid clinical improvement, the development of delayed hypersensitivity to four additional antigens, and the return of lymphocyte counts and proliferative response to normal. These findings suggest that increased energy intake rather than transfer factor therapy was responsible for the child's recovery, and they emphasize the importance of adequate nutrition in the maintenance of intact cellular immunity.