Gallium chest scans of 575 patients were analyzed for their clinical usefulness in conjunction with chest radiographs. The series included patients with pulmonary carcinoma, lymphoma, tuberculosis, sarcoidosis, pneumoconiosis, and interstitial fibrosis. Gallum scintigraphy does not aid in the differential diagnosis of pulmonary diseases but is helpful in determining (a) the degree of activity of a known disease process: (b) treatment response, dosage, and duration; (c) the spatial extent of the disease; and (d) the presence of unsuspected disease foci hidden radiographically in the mediastinum, behind the heart, or in pleural or parenchymal scars.