The other hazard is to some individuals, the personal tragedies associated with the birth and life of a defective child. The NAS Committee has estimated that in the normal course of events in the next 30 years 100,000,000 children will be born in this country and that there will be among them some 2,000,000 with tangible genetic defects. If 40 r is taken as the radiation dose per generation necessary to double the present “spontaneous” mutation rate, the 10 r 3B dose per generation mentioned in the NAS report as tolerable but not harmless would add in the United States alone 50,000 tangible defects in the first generation and eventually after 20 or 30 generations about 500,000 per generation, i.e., about 16,000 per year. A dose of 0.13 r to the gonads per U. S. generation is estimated to be insured from the present rate of weapons testing. This is estimated to produce in the first generation an additional 650 persons with tangible genetic defects, and if this rate of exposure continued there would eventually after some 20 to 30 generations be 6,500 per generation. There would be in addition about 5,000 embryonic and neonatal deaths, stillbirths, and childhood deaths in the first generation with eventually about 80,000 per generation. There would also be a larger but unknown number of minor intangible defects. Were the dose received by the world as a whole the same (actually it is lower), you would have to multiply all the figures by about 20. In absolute numbers they are large. On the other hand, when one compares them with the 2,000,000 tangible genetic defects which are now occurring in each generation and millions of embryonic, neonatal deaths, stillbirths and childhood deaths from genetic causes, they are a small fractional increase. The effects of medical x-rays could be said to be adding eventually about 1/10th to the present U. S. totaly.while fallout at the present rate of testing would add an increment of 1/300th. 3 LIFE SPAN To the best of our knowledge, except for high level radiation to vital organs, the life shortening effects of ionizing radiation are the result of total-body exposure or they may manifest themselves in succeeding generations as a result of genetic damage. There is considerable experimental data in small mammals on the effects of fairly large single event whole-body exposure, i.e., 100 to 200 r and moregiven either once or repeated. There is considerably less information at smaller dose increments. In general it can be said that with large increments, 100 r and more, there is a curtailmentof life expectancy from the time of exposure by approximately 25% per LD/50. Thus a single dose of 200 r would be expected to reduce an individual’s life expectancy from that point on by roughly 12.5%. With smaller increments, a few r to upwards of 100 r, the effect in experimental animals is less marked. One explanation for this is the possibility of a partially effective reparative process. The curtailment of life expectancyis in these circumstancesa little less than 1% per 100 r. If this holds for human beings an average individual who had accumulatedat the age of 40 years approximately 100 r in increments of several roentgens at a time and who would normally be expected to live another 30 years would lose 3 to 4 monthsof his life span. Thereis no definitive information at low doserates, i.e., 0.1 r per day or 0.3 r per week and less which is in the range of the permissible exposure levels as recommended by the In- ternational Commission on Radiological Protection. A few experiments have been done in mice and rats. In each instance the average life span of the irradiated group was slightly higher than that of the control. It appears, however, that the sparing effect is during middle life, and per- haps, chronic low level exposure has some sort of nonspecific effect by permitting survival of experimental animals in the presence of certain ectoparasites. The longer-lived animals in the irradiated group did not live any longer than the longer-lived animals in the control group. In any event, a dose rate of 0.1 r per 30 year period would reduce the average life span by less than a day. While the dose rate of 4 r per thirty year period from diagnostic x-rays might curtail the average life span by at most 2 or 3 weeks. 4 LEUKEMIA The present leukemia rate in the United States is approximately 11,400 cases per year. It is an established fact in many experiments done on animals that large doses of radiation do induce leukemia. In some experiments, although the total number of cases was not increased, 279 oe