Recent interest in whole-body irradiation of human beings, for example prior to bone marrow transplantation in cases of acute leukemia, has led to studies of suitable facilities to provide uniform dosage (1). While ideally it would seem best to irradiate the whole body at once, patient comfort, length of time of irradiation, and economy of space and equipment must be considered. Methods that have been used or proposed include treatment at a long source-skin distance (SSD) to obtain a sufficiently large field, with or without the patient curled into a small space (2,3), and the use of as many as eight Co60 sources of comparatively low strengths (4). These methods have the disadvantage of requiring a large space devoted specifically to this purpose and generally involving a long irradiation time. There would appear to be little objection to the use of a moving-field technique as long as the treatment time were not unduly protracted. This paper describes such a technique allowing a uniform high dosage to be given in a comparatively short time to a patient lying on a conventional treatment couch or hospital bed. The method involves the use of a standard Co60 therapy unit which is normally employed for routine work in the department. Due to the particular suspension system of this unit, the necessary modifications were of an extremely minor nature and treatments can be undertaken with little disruption of the routine schedule for the unit. The unit is made to scan the length of the patient, providing effectively a “;line”; source of radiation at approximately the usual treatment distance. The output becomes dependent not on the inverse square but the inverse first power of the SSD. Depth doses and isodose curves have been measured for stationary and scanned fields. A considerable increase in field size and output can be obtained by removing the collimator from the unit. This is fairly readily done on the unit used in these studies, but some sacrifice in field uniformity results. Depth doses and isodose curves have also been determined both with the collimator removed and with a special “;scan”; collimator in place. In addition, an investigation of dose homogeneity has been made with reference to an assumed body shape. DESCRIPTION OF APPARATUS The Ontario Cancer Institute has a Picker C-3000 teletherapy unit (Fig. 1) which is suspended from a carriage running on rails fastened to the ceiling of the treatment room. This suspension device is made commercially for the Picker X-Ray Company by the Acme Machine and Electric Company of Saskatoon, Saskatchewan, and is preferred in this Institute because it leaves the floor area free of equipment. The three motions of the head of the unit—rotation, elevation and translation—are normally controlled from a pendant hand switch. For whole-body or large-field treatments, remotely controlled translational motion over a length of up to 185 cm., with a constant speed of 2.95 cm. per second and with an unlimited number of reversals, is possible. The maximum length of the scan is limited only by the size of the room. As a result, an effective line source and a long uniform radiation field are produced. The source, containing 3,000 curies, gives an output of 100 r per minute at a distance of 80 cm. With a conventional treatment couch, a maximum SSD of about 120 cm. is available. If needed, greater distance could be obtained by placing the patient on the floor. For this study an SSD of 100 cm. has been chosen and the maximum field size obtainable with the Johns-Mackay collimator (5) is then 25 × 25 cm.