Abstract: A method and apparatus for evaluating the performance of diagnostic x-ray systems. The method consists of using an x-ray generator under standard conditions and making a test x-ray film, for example, of the dental intra-oral type and comparing its density with a calibrated step density strip, using a test tool member consisting of a sleeve-like body with opaque parallel flat top and bottom walls receiving the step density strip slidably therebetween. The flat walls have registering transverse rectangular windows, in the forward parts of which can be exposed a selected density step. The rear portion of the body, between the flat walls, has spacer blocks defining therebetween a transverse channel overlapped by the windows through which the test x-ray film can be inserted to compare its density with that of the selected step density. This can be utilized to determine if the test film density is within an optical density in a desired range including certain steps of the calibrated density strip.