The roentgen examination of the chest is one of the most useful and widely employed tools in present-day medicine. It therefore becomes imperative that one understand its limitations as well as its positive values. Studies have been made of the subjective evaluation of chest roentgenograms (1, 5, 6) on the basis of a series of tuberculosis survey films interpreted by a group of experienced observers. Each member of the group made two or more interpretations of the roentgenograms independently at intervals of several months, and these separate interpretations (intra-individual) were compared. In addition, the interpretations of each individual in the group were compared with those of his colleagues (inter-individual). Not only did these studies show a considerable inter-individual variation in interpretation, but, more important, they revealed an intra-individual variation of 20 per cent. Attempts at an objective evaluation of the examination itself have been made by Rigler, who states that a nodule 3 mm. in size can be detected in a technically good roentgenogram of the chest (17). This observation has been confirmed by Newell (15), at Stanford University, using physical objects of different sizes, shapes, and densities. Both of these studies were concerned with the small or minimal detectable lesion or object. Robbins (18), on the other hand, states that occasionally a lesion as large as 1 cm, in size may not be visible on the roentgenogram. For years, we have been cognizant of the fact that the pathologists observe lesions in the excised lungs that we could not demonstrate upon antemortem roentgenograms. In 1944, therefore, we began to make a series of postmortem roentgenograms of the chest. These were then compared with the antemortem studies as well as with roentgenograms of the excised lungs. We were amazed to find not only that we were missing many small lesions but that in certain instances relatively large lesions were not seen, even in a restudy of the antemortem films. The scope of these studies has now been extended in a number of ways, including the radiography of operative specimens in which a similar experience has been encountered. Descriptions of postmortem roentgen examinations have been published by others, initially by Allred and Garland (1) in 1935, later by Birkelo and Brosius (5) in 1938, and Beilin (3) in 1951. Our technic has improved with experience. The roentgenograms are made in the position employed for the living subject. The examination is made, therefore, in the erect posture. This is accomplished by suspending the body by means of an orthopedic traction apparatus with chin and occipital straps and buckles, connected to a metal cross bar with different slots for heads of different sizes. A wide canvas strap is placed beneath each axilla and connected to the side arms of the suspension bar.