A new DR system using a large-area flat panel detector (FPD) with a 40 by 30 cm active area and a 194 micrometers pixel pitch, has been developed to compare with a conventional image intensifier and charge-coupled device camera type DR system. After measuring basic characteristics of the new DR system such as signal-to-noise ratio, modulation transfer function, and detective quantum efficiency, we applied the FPD to a Gastro-Intestinal study with contrast media, and discussed its potential for clinical use with a medical doctor. In radiography mode, the new DR system with a large-are FPD has superior image quality compared with the conventional I.I.- CCD camera type DR system because of high SNR and DQE. In fluoroscopy mode, the SNR of the new DR system at the exposure range of over 2(mu) R/frame is similar with the conventional I.I.-CCD camera type DR system. As a result, we considered that new DR system with a large-area FPD could be applied to a clinical study replacing an I.I.-CCD camera type. In the evaluation using various clinical images taken with the new DR system by a medical doctor, the new DR system with a large-are FPD performed sufficiently for a GI study.