It is essential in rotational therapy that the radiation beam should strike the area to be treated without error; otherwise, this procedure loses its significance and becomes injurious rather than beneficial to the patient. Accurate knowledge of the size and location of the lesion in the cross section of the body is thus essential. Once this is obtained, it becomes possible to center the lesion accurately in relation to the rotating radiation source and determine the size of the radiation field. The rotational therapy unit in the hospital of the University of Nagoya (Japan), housing a 2,000-c cobalt-60 source, was constructed for irradiation of patients supine upon the therapeutic table. As a first step in the procedure, a roentgenogram is obtained of the cross section of the patient in this same position. For this purpose we have constructed a “universal rotatograph” (1). This apparatus (Figs. 1 and 2) consists of a rectangular iron frame, with a rack for installing the tube (T1) on the upper part and a rack for the film (F) on the lower. Unattached to this rectangular frame, and almost vertically below the x-ray tube, is the radiographic table (B), the structure of which is the same as that of a therapeutic table. Attached to the lower part of the vertical frame is a rotating axis (C) affording free rotation through o to 190°. The film (F) is rotated simultaneously with this. Rotation is accomplished at uniform speed by an electric motor (M). The focal spot of the x-ray tube, the rotation center of the frame, and the rotation center of the film are contained in a plane. The tube (T1) is set in such a position that the central beam makes an angle of 20° with the film surface. Though the frame rotates freely, the x-ray table remains at rest during radiography. With the patient on the roentgenographic table in a posture similar to that for therapy, necessary adjustment is made so that the lesion will be in the vertical plane containing the rotation center, C, of the tube T1. A second x-ray tube, T2, serves for checking this. The patient is asked to hold his breath. The x-ray tube T1 is then rotated through the full scale around the patient, and during this rotation exposure is made. For a film of the pelvis in an adult the factors are 85 kv, 30 ma, 8 seconds; the distance between the x-ray tube and the rotation axis (C) of the frame is 148 cm., and that between the rotation axis and the center of the film 46 cm. Under these conditions an axial transverse laminagram (2–5) is taken. The x-ray image thus obtained is similar in shape to the actual cross section of the body. There is no distortion, except for the magnification (× 1.3). The layer of the cross section visualized is considered to be about 0.5 mm. thick. Thus the contour of the cross section of the body and the actual, or at least suspected, status of the lesion are revealed, and the distance of the lesion from the surface of the body in the sagittal and frontal planes can be measured.