head. After the atomic bombings, many of the most severely irradiated survivors experienced various degrees of temporary epilation because of damage to the hair follicle cells. That subtle permanent damage to the hair might result is a reasonable postulation. Such damage might be manifested by accelerated hair graying unrelated to general aging acceleration. Since increased hair pigmentation sometimes has been noted in therapeutic irradiation in human. beings,* damage might even be evident through an increase in age at the onset of hair graying. Both skin aging and hair graying are amenable to certain simple, semiquantitative estimates that can be carried out during a clinical examination. Several tests were performed on a sample of irradiated and nonirradiated subjects undergoing examination at ABCC in Hiroshima. The findings have been analyzed in relation to radiation exposure. Methods Composition of the sample. The measurements were carried out during standard clinical examinations on radiation exposed and nonexposed subjects who are voluntarily participating in the continuing adult health study at ABCC in Hiroshima. The sample consisted of 4 different “exposure” categories: Group | consisted of proximally exposed persons, less than 2,000 meters from the bomb hypocenter, who had experienced acute major radiation damage in 1945. This damage had been manifested by epilation, purpura, or oropharyngeal complaints suggestive of agranulocytosis. 28 Group 2 was made up of proximally ex- posed persons, under 2,000 meters from the hypocenter, who had not experienced symptoms indicative of major radiation damage. Group 3 was composed of distally exposed persons, between 3,000 and 3,500 meters from the hypocenter, who were beyond the area of radiation but within the area of blast and other damage from the bomb. Group 4 comprised nonexposed immigrants who had entered the city from 1945 to 1950. In essence, then, the 4 groups repre- sented: (1) the most heavily irradiated, (2) the moderately irradiated, (3) intrinsic controls, and (4) extrinsic con- trols. The 4 groups were carefully matched as to age and sex composition, and representative subsamples of the total were brought to the clinic monthly over a twenty-four-month cycle. This mechanism assured that a study conducted on a few hundred subjects would be generally representative of the whole sample in regard to age, sex, and exposure group. Figure I represents the age and sex composition of the entire adult health study sample in Hiroshima. Unusual features of its composition reflect the fact that many children had been evacuated from the city at the time of the bombing and that many young men were away from the city serving in the armedforces. ete cent oF WOTsame ce et® Ces? or TOTAL Samryt is 1% a Hair graying is particularly interesting as a late radiation sequela because of the sensitivity found in the melanin-producing cells of the hair follicles in irradiated rodents*—a sensitivity, however, which has not been noted in human beingsreceiving therapeutic irradiation to the | ° x AGE AT Time oF goue FIG. 1. Age and sex composition of entire adult health study sample in Hiroshima. GERIATRICS, JANUARY 1961