in Hiroshima and Nagasaki to parents who were related as first cousins, first cousins once removed, or second cousins. There are a number of reasons why the geneticist is inclined to view the latter pregnancies of related parents as potentially a more sensitive index of radiation-induced genetic damage. In its simplest terms, the main line of the argument is that the addition of radiation-induced mutants to the more homozygous, and presumably less elastic, genetic background of inbred children may produce a relatively greater effect than would be apparent if the same mutants were super-imposed on the more heterozygous genetic background of noninbred children, that is, children born to unrelated parents. It seemed unwise, therefore, in the analysis of the data from Hiroshima and Nagasaki, to simply pool the present observations with those on noninbred children, particularly since the inbred children were not uniformly distributed over the various exposure classes to be described shortly. The present report serves then to complete the picture of the effects of parental exposure to the atomic bombing of these two cities.

Brief Description of the Program—In the years immediately following World War II, a ration system existed in Japan which permitted pregnant women to acquire certain rationed items by registering the fact of their pregnancy some time after the fifth month of gestation. The economic milieu of Japan in this period was such that registration was virtually complete. There existed, then, a set of circumstances which afforded an opportunity to launch a comprehensive prospectively oriented study of pregnancy terminations following parental irradiation. With the cooperation of the municipal authorities in Hiroshima and Nagasaki, a system was instituted in 1948 whereby at the time of her registration for rations, each pregnant woman or her representative also registered with the Atomic Bomb Casualty Commission (ABCC), an agency of the National Academy of Sciences-National Research Council working in cooperation with the National Institute of Health of Japan. At the time of registration, the first two-thirds of a questionnaire was completed which included such items as identifying information, a brief radiation history of the husband and wife, a short summary of the past reproductive performances, and pertinent details concerning the present pregnancy. Upon the termination of the pregnancy, the attending midwife or physician notified the ABCC, and completed the previously mentioned questionnaire. Irrespective of the type of termination, a Japanese physician in the employ of the ABCC or the Japanese National Institute of Health called to examine the child as promptly after birth as possible. The completeness of this system of reporting and follow-up was checked periodically; these checks revealed that approximately 93 per cent of the births occurring in Hiroshima, and a somewhat higher figure in Nagasaki, were known to the commission. A large proportion of the 7 per cent not ascertained through this scheme subsequently came to our attention through other channels. The latter, unregistered births, while not included in the results to be reported, permit an appraisal of the representativeness of the registered births.

In the event that a pregnancy terminated abnormally as in a stillbirth or a child with a congenital malformation, a supplementary questionnaire was completed in the patient's home by the examining physician. This questionnaire was designed to obtain more detailed information on the gynecologic history, maternal illness during pregnancy, past reproductive performance, and economic status. In addition to this questionnaire, blood was drawn from the mother for a serological test for syphilis (on the average, some 5 per cent of these tests were positive). The same supple-