Two patients under long-term surveillance showed the similar clinical features of low-grade fever, scanty productive cough, progressive dyspnea, and roentgenologic findings of lung infiltrates. Both patients responded only to systemic corticosteroid therapy and suffered relapses when it was discontinued. In one patient, who was found to be IgA-deficient, the pulmonary disease followed an episode of subacute thyroiditis; in this patient the intake of cephalosporin and subsequent rechallenge with the drug aggravated the disease. Needle biopsies in both patients showed the features of organizing intra-alveolar pneumonia. The histopathologic findings and their relation to the clinical symptoms are discussed.