In a series of 496 rheumatoid spondylitis patients treated with x-ray, the authors have reported an incidence of leukemia over 17 times greater than expected in a comparable population. No conclusion can be drawn with respect to the exact nature of dose-response relationship in leukemogenesis. Four of the reported leukemias arose from myeloid reticular elements of the bone marrow; the fifth case is of undetermined origin. Since the chief use of x-ray therapy under these circumstances is as an analgesic, it would seem unwise to compound the risk of developing leukemia in these patients by its continued use unless all other forms of symptomatic treatment have failed and the patient and the physician mutually accept the possibility of this increased hazard.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/37686/1/1780030108_ftp.pd