Intestinal lymphoid hyperplasia and recurrent pulmonary infections by pyogenic bacteria are well-recognized accompaniments of common variable (late onset) hypogammaglobulinemia. A 35-yr-old woman with this illness had progressive pulmonary insufficiency caused by nodular lymphoid interstitial pneumonitis, rather than by infectious lung damage, and intestinal lymphoid nodular hyperplasia. B cells were abundant in the intestinal nodules but absent in the pulmonary nodules by immunoperoxidase staining. Pulmonary lymphocytes isolated in single-cell suspension from the biopsy were 0.5% B cells and 82% T cells. Prednisone therapy improved pulmonary function and decreased the intestinal lymphoid nodules. Lymphocytic interstitial pneumonitis should be considered in patients with hypogammaglobulinemia and restrictive lung disease.