Although differences in incidence of various Table 11 Relationship of Radiation Exposure to Infection With Intestinal Parasites Organism Exposed (69 cases) Unexposed (112 cases) Totals (181) Entamoeba arstolytica Entamoeba histolytica (small race) Entamoeba colt Endolimax nana lodamoeba butschtit Giardia lamblia Chilerastix mesnilt Trichomonas hominis Hookworm 14(20.3)* 19(16.9) 33 (18.2) 2 (2.9) 25 (36.2) 14 (20.3) — 5 (7.2) +. (5.8) 24 (34.8) 2 (2.9) 10 35 35 3 9 4 30 8 12 60 49 3 14 8 54 10 No parasites 11 (15.9) 30 (26.8) Trichurts trichiura 21 (30.4) (8.9) (31.3) (31.3) (2.7) (8.0) (3.6) (26.8) (7.1) 41 (36.7) (6.6) (33.1) (27.1) (1.7) (7.7) (4,4) (29.9) (5.5) 62 (34.3) 41 (22.7) *The numberin parenthesesis the percent. highest incidence, 26.8%, was found amongadults in the 21 to 50 age group. The other twointestinal amebae, Entamoeba colt and Endolimas nana occurred much more frequently in the youngest age group, 23.3 and 18.6% respectively, and both showed increases among the older individuals. Among flagellates, the Giardia lamblia incidence washighest in the young children and almost nonexistent after the age of 12. T. hominis showed high, relatively unchanged incidencein all age groups. Of the two helminths found, hookworm showed a steady rise in incidence, from 2.3 to 12.5%, with ages up to 50. No infections were found after 50 years of age. T. trichtura occurred in 30.2% ofthe children 5 years old or less, and in 66.7% of the 6 to 20 year group. In the older age group, 21 to 50, the incidence dropped to 16.1%, rising again after 50 to 31%. Table 14 shows a breakdown ofinfectionsac- cording to sex, with a further division into two age groups, less or more than 13 years of age. Division into the two age groups was madeon the basis that both sexes probaly engaged in similar pursuits up to puberty, but that afterwards their daily routines probablydiffered. Older males had higherinci- dences than older females, or similar ones, for all parasites except J. trichiura, the incidence of which was about half as great in males. Among younger males, incidences tended to be lower than among young females, except that of E. colz, which was distinctly higher in the males. S007Z44 parasites occurred in exposed and unexposed groups, there is no convincing indication that radiation had anything to do with the variations. In most instances differences can be accountedfor by samplingerrors in the relatively small numbers of cases studied. In addition, the two groupsare not precisely comparable. The unexposed or control group consisted of individuals who had lived on different islands before joining the exposed population of Rongelap. Environmentalsanitation had not necessarily been the samefor the two groups. The environment on the coral atolls and the customsofthe inhabitants are such that it was not expected that any trematodeorcestodeinfections would be found. However, the complete absence of Ascaris in the face of a 34.3% incidence of Trichuris was unexpected. Life cycles of both these nematodes in the external environment are such that they are customarily found together. The history of Marshallese association with other peoples, Europeans, Japanese, and Americans, makes it likely that they have been exposed to Ascaris. Thus, oneis led to the possibility that the external environment on Rongelap Atoll maybe unfavorable for Ascaris even though very suitable for Trichuris. It was not possible to obtain stools from any of the few dogs on theisland in order to check for dog ascarids. Several dried pig droppings were examined at one time and no Ascaris was found in them. However,in the absence of more epidemiological and experimental information, one can only guess the reasonsfor the lack of Ascaris. Soil moisture, salinity, pH, porosity, etc., may all play some part in this unusual picture. The fact that half the cases with eosinophilia showed no helminthic infections at all suggests other significant factors causing this blood picture besides parasitic infections. On the other hand, the greater incidence of Trichurts among Marshallese with eosinophilia than among those without eosinophilia indicates that infection with that helminth may have been a contributing factor in its incidence. The incidence of parasites in all age groupsindicates that fecal contamination is widespread and that infections are acquired early in life. Although individual Marshallese were generally neat and clean in appearance,their simple sanitaryfacilities andrural life makeit likely that fecal contamination is a continuing affair. The concentration of