containing 1.5 ml of newly mixed merthiolate-iodine-formalin (MIF) (70) and thoroughly comminuted to ensure adequate fixation. The preserved samples were transported to the Tropical Infectious Disease Research Program Laboratory, U.S. Public Health Service Hospital, New Orleans, LA, where they were examined both by a standardized direct smear method (2 mg) and by an ether concentration technique using the entire sample. Treatment. Treatment on Rongelap consisted of mebendazole, 100 mg (one chewable tablet) twice daily for 3 days, monitored either personally by che survey physician or under his supervision by the island Health Aide. At least 902 of the inhabitants present during the quarterly visits and eligible for treatment (pregnant women and children aged <2 years were excluded) were so treated at the scheduled quarterly intervals. Treatment on Utirik with pyrantel pamoate suspension, 10 mg per pound body weight, single dose, was given to at least 90% of the eligible inhabitants present during the quarterly visits indicated in Table 1. Body weight was determined with a portable scale. Coverage of the population was attained by using survey lists and by many miles of footwork on this -.elatively small island. C. Results and Discussion Intes<inal Protozoa - Rongelap and Utirik Atolls. Intestinal protozoa observed during the list survey on Rongelap Atoll (September 1979) included amebae (not differentiated into pathogenic and non-pathogenic species) in 26.5% of specimens, and Giardia lamblia in 17.6%; no Balantidium coli were seen despite the l:rsge number of free-roaming pigs on the island. Intestinal protozoa found in Utirik Atoll inhabitants in September 1973, concurrently with a minor epidemic of mild diarrheal disease, included amebae in 7.6%, Giardia lamblia in 5.1%, and Balantidium coli in 7.6%, the Giardia and Balantidium being present in surprisingly large numbers in some specimens. Amebae identified included Entamoeba histolytica (cysts and trophozoites), Entamoeba coli, and Iodamoeba butschlii. It must be stressed that, since the survey was concerned almost exclusively with intestinal helminths, wherea» MIF is not the field fixative of choice for direct observation of protozoa, these results cannot be considered definitive. Nevertheless, the presence of the primary protozoal pathogens, Giardia lamblia, Entamoeba histolytica, and Balantidium coli, on Utirik Atoll was verified under circumstances not inconsistent with their being involved 1n the etiology of the diarrhea observed. During the November 1980 survey, appropriate materials for surveying protozoa will be included. Intestinal Helminths - Rongelap Atoll. Intestinal helminths found in Rongelap Atoll inhabitants before and during the period of suppressive treat- ment with mebendazole are listed in Table 2 (A and B) (71). As in 1958, Trichuris trichiura was the most prevalent parasite detected. At the start of the current survey in June 1977, 73.02 of the popula— tion tested (163) was infected, including 80.2% of children (96) and 62.4% of adults (67); this represents a greater than twofold increase since the 1958 survey. - 38 -