Immunologic factors have been incriminated in the pathogenesis of lymphoid interstitial pneumonia. The discovery of a patient with coexistent lymphoid interestitial pneumonia, pernicious anemia, and common variable hypogammaglobulinemia focused attention on the possible autoimmune nature of this pulmonary disease. Extensive immunologic studies demonstrated a noticeably impaired bonemarrow-dependent (B cell) system and intact thymus-dependent (T cell) system. No evidence of humoral or cellular hypersensitivity to homologous lung determinants was found.