The fundamental principles of different methods of foreign body localization were nearly all set forth within a few years after the original discovery of x-rays. The extensive literature on the subject since then has dealt chiefly with modifications or refinements of technic to overcome some shortcoming or to fill some special need. (For a summary and bibliography see the appended references.) Practically all of the fluoroscopic methods either have been developed for the purpose of facilitating work in a military hospital or require special apparatus or attachments, or some preliminary calibration. There is need for a simple method which can be used in civilian laboratories employing only the materials generally at hand and without any special arrangements or preparatory adjustments or settings of the apparatus. The method to be described here requires only a standard table fluoroscope and the ordinary parallel arm caliper used in most laboratories to measure patient thickness. The method is a refinement ...