Patients with mild symptoms or pulmonary function abnormalities (such as a decrease in diffusing capacity of o20% from baseline or no change in oxygen desaturation during exercise), or with transitory or slight radiographical infiltrates are monitored using pulmonary function tests, symptoms and usually CT scans. Diagnostic evaluation and treatment for drug-related lung disease is considered in those patients who experience dyspnoea at rest or on mild exertion, have a X20% decrease in carbon monoxide diffusing capacity, or experience oxygen desaturation at rest or during exercise. Patients whose radiographical infiltrates are extensive or progressive are also considered for therapy.