Two patients with gastrointestinal tract abnormalities were discovered to have significant defects in both humoral and cellular immunity. Patient 1, a 4-year-old girl with suspected food allergy, failure to thrive, and chronic diarrhea, exhibited a decreased serum IgG immunoglobulin level, decreased numbers of peripheral blood T lymphocytes (erythrocyte rosettes), decreased numbers of T-lymphocyte subpopulations (T3+, T4+), decreased responses of lymphocytes to common mitogens, and absent in vivo responses to delayed hypersensitivity skin test antigens. Patient 2, a 3-year-old girl with chronic anemia, presented with immunological abnormalities similar to those of patient 1. On investigation, both patients were found to have significant structural abnormalities of the gastrointestinal tract. Patient 1 had a malrotation of the small bowel, while patient 2 had a cavernous hemangioma of the mid-jejunum. Following surgical correction of the gastrointestinal abnormalities, there was improvement in all immunologic values. By ten to 18 months after surgery, both patients demonstrated normal immunological function. Thus, anatomic lesions of the gastrointestinal tract that mimic more common childhood disorders, such as food allergy and anemia, may produce serious states of secondary immunodeficiency.