We report the beneficial effect of steroids in a 27-year-old woman with lymphocytic interstitial pneumonitis (LIP) and common variable immunodeficiency (CVID). Exertional dyspnea, x-ray infiltrates, and pulmonary physiologic abnormalities decreased or increased during 3 1/2 years of follow-up in parallel with the administered dose of prednisone. This observation rules out concomitant spontaneous remission as the explanation of steroid-induced improvement of LIP in CVID. Steroid treatment was apparently safe: the frequency and severity of recurrent bronchial infections did not change, although IgG replacement therapy was not provided.