Dynamic chest radiography using a flat panel detector (FPD) with a large field of view is expected to be a useful pulmonary functional evaluation method based on the respiratory changes in pixel value. For clinical use as a follow-up and therapeutic evaluation tool, the system must have a high degree of reproducibility in measurements of pixel values. The present study was performed to investigate the reproducibility of respiratory changes in pixel values. Dynamic chest radiographs of five normal subjects and one patient were obtained. Imaging was performed twice in each subject. The slope (X-ray translucency variation) was then calculated from the changes in pixel value from distance lung apex-diaphragm, and the slopes of two sequences were compared. The results showed there were no significant differences in changes in pixel value between the two sequences in all normal subject (5 males, p>0.05). The results indicated that the present method has reproducibility for measuring pulmonary function and also has potential as a tool for follow-up and therapeutic evaluation.