Twenty patients with pulmonary nodules consisting of concentric hyaline lamellae, usually accompanied by perivascular collections of plasma cells and lymphocytes, were studied. In most instances, the lesions were multiple, bilateral, and mildly symptomatic. Many of these nodules showed all of the staining characteristics of amyloid, but others had an atypical birefringence pattern. No infectious agents were identified, and no consistent pattern of dysproteinemia was observed. Two of the patients had prior histories of tuberculosis. In other cases, the nodules were of unknown origin and pathogenesis. Four cases were complicated by sclerosing mediastinitis, and one, by retroperitoneal fibrosis and amyloidosis. Our current working hypothesis is that these lesions represent an exaggerated and, possibly, continuing immune response, perhaps to one of a number of agents.