Image intensifiers are now beyond the realm of experimentation and have become an integral part of the routine equipment in diagnostic radiology. Since the day of W. E. Chamberlain's Carman Lecture, “Fluoroscopes and Fluoroscopy” (1), the need for raising image brightness to cone vision level has been generally recognized. The Westinghouse Corporation in 1949 produced the first practical model of the Coltman image-intensifier tube; Chamberlain, in our institution, Temple University, used this in clinical work. Since that time our interest in image intensification has continued and we have had many tubes available for clinical and experimental purposes. In the desire to standardize photographic procedures utilizing the image-intensifier tubes, we intercompared tubes and evaluated their responses. The data and conclusions that follow are based on both the physical and the practical operating aspects of the tubes tested. The image intensifier is a large vacuum tube containing at the x-ray input end a fluores...