The routine chest roentgenogram is standardized as upright postero-anterior teleroentgenogram with half inspiration, but in impossible cases, such as infants, children and severe illed patients, the supine chest AP view have to be taken. There are many different points between upright chest PA and supine chest AP view. Authors analysed the 51 cases of normal upright chest PA and supine chest AP views which were taken in the same people, same exposure factors and the same tube-film distance of 72 inches. The results were as follows: 1. The width of the mediastinum was wider in the supine chest AP view than the upright chest PA view, 6.60$pm$1.36cm, respectively. 2. The diameter of right descending pulmonary artery was slightly smaller in the supine chest AP view than the upright chest PA view. The distribution of the pulmonary vasculartures was nearly even in the supine chest AP view. 3. The transverse diameter of the thorax was slightly smaller in supine chest AP view, but the t ansverse diameter of the heart was significantly increased in the supine chest AP view. The transverse diameter of the heart was 12.12$pm$1.5cm in upright chest PA, and 13.12$pm$1.63cm in supine chest AP, respectively. 4. The cardiothoracic ratio was markedly increased in supine chest AP than the upright chest PA view. the cardiothloracic ratio of the upright chest PA was 43.72$pm$3.97%, and in the supine chest AP, it was 48.19$pm$4.73%. 5. The supine chest AP view of this study is different in tube-film distance from the routine portable films of the chest AP view, and the magnification factors are probably different. Further studies are need.