While methods of testing fluroscopic systems are well established, using test objects such as the Leeds test objects, observer influence may affect the results and the process is relatively time consuming. An alternative approach is examined, whereby use of a line selector and oscilloscope are used with a test object to examine resolution, contrast and grey scale steps. Three radiotherapy simulator fluoroscopic imaging systems are tested and, in each case, observed images are found to be limited by the signal response, as present in the video signal, and not by monitor performance. Edge enhancement effects and signal droop are also found to be effects which merit further investigation. It appears that, at low cost, the use of an oscilloscope and a TV line selector may permit the development of quantitative methods for assessing the performance of imaging systems.