It is generally assumed that adult height is attained when the skeletal age is 17 to 18 years in girls and 18 to 19 in boys (50,52,248), but actual measurements on the Marshallese population showed that many subjects continued to increase in stature with advancing chronological age, even after age 30, although the late increments were almost always very small. After the Marshallese reached age 16, absences from the island at the time of survey became more frequent; therefore, the time when adult stature was actually attained is uncertain for many individuals. Statistical analyses (Appendix III) of the data. on adult (final) stature of the Rongelap inhabitants who were in the pediatric age group on March l, 1954, gave the following results: * In the unexposed group, for both boys and girls, there was no significant difference in mean adult stature between those born after 1944 (<10 years old sn March 1, 1954) and those born before 1945 (>10 years old on March 1, 1954). * In the exposed group, for both boys and girls, there was no significant difference in mean adult stature between those born after 1944 and those born before 1945. * For both boys and girls, there was no significant difference in mean adult stature between those who were exposed on Rongelap and Ailingnae to fall- out radiation and those who were not. Since osseous maturation is dependent on normal thyroid function, it is reasonable to assume that its retardation in exposed children was due to radiation damage to the thyroid glands. The marked retardation of skeletal matura- tion followed by dramatic improvement after the administration of thyroid hormone has been documented in the children who were clinically hypothyroid (13). The catch-up phenomenon in respect to osseous maturation can reasonably be attributed to the administration of thyroid hormone to the exposed popula- ~~! J af C3 cu ora] oy tions, many of whom were subclinically hypothyroid (see Section IX.C.2). - 31 -