other years through simple random variation. The same random variation applies to the number of genetic defects that might appear in any arbitrary group of 12 births. In accordance with Roger Ray's suggestion to compare the anticipated effects of radiation levels at Bikini with those of high background areas in the United States, we might mention that Denver, Colorado has a population of about one-half million residents who are exposed to a natural background level averaging 160 mrems. No unusual genetic or cancer incidence has been observed in the Denver population or in the populations of other states having high average altitudes. Such comparisons are not conclusive, however, because socioeconomic and genetic differences may affect cancer rates and, possibly, the incidence of genetic defects. With this information, we hope that the people of Bikini will be in a better position to compare the health cost that may result from a return to the Atoll with the benefits to be derived from their return.