Clinical, radiographic, and histologic data, together with pulmonary function features, in eleven patients with cryptogenic fibrosing alveolitis, are described in the following study. All these patients presented with a history of exertional dyspnea. Eight of the eleven had radiographic evidence of pleural involvement as manifested by blunting of one or both costophrenic angles. A restrictive defect was present in eight patients, all of whom had x-ray changes showing diffuse involvement. One of the patients presented showed marked improvement in all parameters including a repeat lung biopsy. Immunofluorescent studies of the lung biopsies from six patients revealed no evidence of immunologic damage. Based upon the histologic pattern of pulmonary reaction in the biopsies and the intervals between the onset of symptoms and the time of biopsy, a tenative scheme of temporal evolution of this disease is presented. Lung injury may lead either directly to diffuse interstitial pulmonary fibrosis (DIPF) or lungs may react to injury by an initial alveolar, mural or mixed pattern, all of which might ultimately progress to DIPF. An initial alveolar or mural pattern might change to a mixed pattern.