The energy subtraction (ES) method is an image processing technique that depicts a radiograph from which the image of intentionally specified tissue has been eliminated. The ES radiograph is usually obtained by subtraction of two x-ray images taken for two different values of tube voltage, owing to inherent energy dependence of the attenuation coefficient of each tissue. Since white x rays are, generally used in the ES method, the beam hardening occurs during x-ray penetration through a subject, resulting in discrepancies among x-ray absorption ratios even for the same tissue depending on its location in the subject. This brings erroneous information about the attenuation coefficient also in the ES method. Therefore, a new ES method was examined using dual energy x rays with the same beam hardening characteristics. As a result, this ES method suggested the high power to discriminate materials and its usefulness in radiological diagnoses as compared with the usual ES method using white x rays.