Most roentgenologists have long recognized the need of reliable quantitative data giving the speed, detail, and contrast characteristics of commercially available roentgenographic films and intensifying screens. From such information, the choice of the most satisfactory films and screens for use in a roentgenographic department may be greatly facilitated. Furthermore, the availability of such information to the profession would constantly stimulate the x-ray industry to improve the quality of its products. Before quantitative data listing the characteristics of films and screens can be made generally available to the radiologist, however, four fundamental steps must be taken. First, standard definitions of speed, detail, and contrast must be established. The terms of these definitions, of course, should correspond as closely as possible to the conditions which occur when the films and screens are used in normal roentgenographic practice. Second, methods of measurement which comply with the standard defini...