Recently, in connection with an ongoing medical study of certain Marshall Islanders prompted by the Bikini incident (1), we have had the opportunity to examine a sevies of blood samples from these Islanders Pan tie ocenrrence of both polymorphisms and rare variants of serum prateing and erythrocyte enuynes. The results, when treated in the USUAL fashion and comb ined with the findings of others on Micronesians, . . there may be susgest/& lower frequency of rare variants in this group than in such groups as Japanese, Caucasians, or South American Indians. There are seme bothersome problems in comparisons across groups sampled in different ways, however, which make the usual statistical contrasts impossible; some of these problems are aired, THE POPULATION The study population is composed of persons now residing on Ebeye, Rongelap, and Majuro Islands, for the most part related to one another as embers of nuclear families. The number of independent genomes in the sample is thus considerably less than the number of persons. Approximately half of the children in the sample were born to parents inadvertently radiated as a result of fall-out from a nuclear explosion at the time of the Bikini test, in 1954. However, as will be apparent under RESULTS, the question of a radiation effect will not arise in any substantial manner. a TTT