A 48-years-old patient with a clinical picture of dyspnea, unproductive cough, and nonspecific thoracic pain is reported. The most outstanding finding in the physical examination was the auscultation of fine crepitants after inhalation, located in both pulmonary bases. The chest X-ray desmonstrated the existence of some confluent, bilateral opacities of a net basal predominance, which were suggestive of an interstitial process. The lung biopsy, through a thoracotomy, has allowed for the diagnosis of a desquamative interstitial pneumonia. The alterations found in the humoral immunity, which basically consisted of an important increase of IgG and a less-marked increase of IgA, have shown a regressive tendency, closely correlated to a good response to the steroid therapy. The clinical and roentgenological course of the patient has been similarly favourable.