Four infants presented with the combination of food allergy, transient hypogammaglobulinemia (THI), and elevated serum IgE levels. Food allergy was documented by history, positive skin tests for immediate hypersensitivity, radioallergosorbent test, histamine release studies, and lymphocyte transformation in response to food allergens. THI was probably secondary to decreased production since there was no evidence of protein loss from the gastrointestinal tract. Immunologic studies revealed normal B cell number and function in vitro. T cell number and proliferative response to mitogens and antigens were normal but T cells were deficient in their ability to generate helper factors necessary for B cell maturation into immunoglobulin secretory cells. The THI and the deficient production of T cell--helper factor resolved after the age of 20 to 24 mo. A defect in immunoregulation may be responsible for the immunologic abnormalities observed in these patients and their propensity to develop IgE antibodies to food allergens.