af on Aging and Life Shortening in Human Populations 493 It is believed these cross-sectional studies will be improved with further testing of these populations on a longitudinal basis. The addition of more tests involving organ function would also be desirable. Until we understand more about the chain of events leading to radiation-induced aging, we will probably continue such studies using the empirical approach. Hopefully, they may lead to clues which will suggest more fundamentalstudies. Some Nonneoplastic Late Findings Related to Radiation Exposure Life shortening. As has been pointed out, the role of irradiation in bring- ing aboutlife shortening from the developmentof malignantlesions, particularly leukemia, is well established in animals and man. However,life shortening from otherlate effects is better established in animals than in man. Stud- tes of mortality in medical specialists using ionizing radiations, particularly radiologists, from about 1930 to 1954 have been reported by several investigators [5,13,27,31,32]. During the early years when radiation protective measures were not as good, radiologists received larger amounts of radiations than other physicians. Studies of mortality tables in the various medical specialties showed that radiologists had a shortening of lifespan of about 5 years. Mostof this reduced lifespan was due to leukemia and to a lesser extent to other malignant tumors, but life shortening wasstill detectable from other causes where these malignancies were subtracted. COURT-BROWN and list of natural causes, mortality appears to bear norelation to radiation dos- age. In none of the four time periodsis there evidence of general increase in mortality that one might expect from the hypothesis of accelerated aging.’ In regard to the Marshallese population the numbers exposed are too small to give reliable assessmentof life shortening effects. Lensopacities. Opacities of the crystalline lens of the eyes have been not- ed asa late effect of irradiation in cyclotron workers [1], patients receivingirradiation to the eyes [23] and in the ABCC studies [6, 29]. Such lens changes range from posterior subcapsular plaques and flecks visible only with slit lamp examination to frank cataracts in a few cases with reduced vision.In re- cent studies on the Marshallese people, BATEMAN found an evidence of in- tee ey eRTe Tt ose TD Peeak DOLL [13] in studies not strictly comparable, did not show any difference in longevity in British radiologists. Recently BEBEEet a/. [2] reported on 13,000 deaths occurring between 1950 and 1966 among 82,000 Japanese victims of atomic bomb exposure. They reported ‘...once cancer is removed from the