As is well known, roentgen examination in acute thrombosis has been based mainly on venography after injection of various opaque media. This latter method has contributed largely to our understanding of the site of origin of the thrombus in the lower extremities. According to Bauer (1) and Hellsten (4), the primary seat of spontaneous thrombosis is in the deep venous trunk of the calf. Here the thrombus has its roots, ascending gradually to the popliteal vein and the veins of the thigh. The venographic examination gives in most cases clear evidence as to the location of the thrombus and the extent of the secondary circulatory disturbances. Generally, however, the use of this method is limited, mainly because it is expensive and not without complications. Injection of the dye must be made with the greatest care, and every precaution must be taken to prevent the medium entering the tissues outside the vessel, where it may produce local necrosis. In general, injection of contrast medium outside the vessels does not lead to necrosis, but in acute thrombosis of the lower extremities the vascular supply of the tissues is apparently compromised beforehand, so that little more is required to bring about inadequate nutrition of the tissue. In a previous paper the writer has described a new method of value for the diagnosis of acute thrombosis, based on the roentgen examination of the soft tissues of the extremities (3). Not only is this procedure very easily carried out, but it can be done on the ward with a mobile unit if desirable. Also, it may be repeated without inconvenience to the patient and used to check the result of treatment. Technic The roentgenograms may be taken when the patient is lying in bed, though better pictures are obtained if he is on a Bucky table. The cassette is placed directly under the calf or the thigh, and the exposure is made so “soft” that the skin is definitely outlined. Usually 40 to 50 kv. and 100 ma. are required; the time of exposure is half a second, and the target-film distance 90 to 100 cm. Care must be taken to check the development of the film and keep the darkening strictly within limits. The subcutaneous tissue, which is the most radiolucent part of the extremity, must have a certain clarity on the film. A 30 to 40-cm. cassette is convenient and should be so placed that the lower part of the thigh is included. When a thrombosis in the middle or upper part of the thigh is suspected, a film should be taken right up to the groin. The other extremity should always be filmed for comparison, both sides being exposed simultaneously. It is emphasized that the lateral border must not be covered or cut off. In thin patients perfect films can be obtained without a grid, but for obese patients a movable grid is preferable. This technic has now been employed in 50 patients with acute thrombosis proved clinically, by venography, or at necropsy.