Ascaris lumbricoides, not found at all in the 1958 study, was detected in 24.5% of those tested, in 1977, including 38.5% of children and 4.4% of adults. Infestation by worms was related to the post-fallout period by the Rongelapese, who appear to give less credence to the concept of introduction being the result of increased inter-atoll contact made possible by the greater availability of Trust Territory shipping. The prevalence of hookworm, detected in only 3 individuals (1.8%), was virtually unchanged since 1958, if the increased potential for absence of study subjects from the island is taken into consideration. Only 23.4% of the population tested appeared to be helminth-free at the beginning of the current study, including 15.6% of children and 34.3% of adults. Effects of Treatment - Rongelap Atoll. Population-wide treatment with mebendazole onRongelap resulted in a dramatic reduction in population worm burden, clearly evident at the interim stool sampling conducted in January 1978, 3 months after the second quarterly treatment (Table 2, A and B). Percent reductions of 79% and 92% of initial worm burdens of Trichuris trichiura and Ascaris lumbricoides, respectively, had been effected, and hookworm was not detected. Of even greater significance is that 9 months after the last (January 1978) treatment course, these reductions were still very much in evi- dence (September 1978). Nevertheless, one year later (September 1979) a notunexpected resurgence of infection had taken place, although the gains effected by the treatment had not been entirely eliminated. Intestinal Helminths ~ Utirik Atoll. Intestinal helminths found in the Utirik Atoll inhabitants tested (>20% of the population) are listed in Table 2 (C and D) (4). As on Rongelap, Trichuris trichiura was the most prevalent parasite, but the level of infection on Utirik was even higher: 91% of the sample tested (24% of the population). Ascaris lumbricoides was present in 25.8% of the initial Utirik samples, a level virtually identical with that on Rongelap before suppressive treatment. The hookworm level on Utirik, only 2.2% positive specimens, was also quite comparable with that found initially on Rongelap. None of the children tested, and only 16.2% of the adults were helminth-free. Effects of Treatment - Utirik Atoll. Population-wide helminth- suppressive measures on Utirik were only against Ascaris lumbricoides and hookworm, and consisted of three treatments (see Table 1) with pyrantel pamoate, an anthelminthic not considered to have any effect against Trichuris. (The trichuricide oxantel pamoate was to have been used in conjunction with the ascaricide pyrantel pamoate, but it was not available because of FDA restrictions on its use in populations under U.S. jurisdiction.) Their effectiveness even against pyrantel pamoate's main target, Ascaris lumbricoides, was disappointing: the reduction was only 21% at 6 months after the first treatment, and only 31% at 9 months after the third treatment (compared with 96% at 9 months after the third treatment with mebendazole on Rongelap). As expected, the trichuriasis level was not reduced, the mean being 93.0% throughout the study. The hookworm level was 2.5% at the conclusion of the suppressive effort. Eosinophilia - Rongelap and Utirik Atolls. Because intestinal nematodes are a common cause of blood eosinophilia, particularly (but not exclusively) during the tissue-migration phase of the parasitic life cycle, peripheral eosinophil counts were correlated with temporal events of the suppressive c ¢ ¢ Kae ~ 40 -