The advantages of high kilovoltage and pulmonary filters in frontal chest X ray are described, underliing the possibility of a simultaneous demonstration of both pulmonary fields and mediastinal structures. A description is given of the most important mediastinal lines and of their semeiological value in pathologic conditions. The excellent results obtained by means of hemifiltration in patients with opaque hemithorax are stressed. An increased diffusion of such technique could be justified by its simplicity, and by the low cost and high benefit.