VI. A. PARASITOLOGIC SURVEYS AND SUPPRESSIVE ANTI-HELMINTH TREATMENT ON RONGELAP AND UTIRIK ATOLLS, MARSHALL ISLANDS, 1977-1979* Background The first formal parasitologic survey within the area exposed to fallout was conducted on Rongelap Atoll in 1958 (14), one year after the return of its inhabitants. At that time, stools from 181 persons were examined by standardized direct saline mounts and by formalin-ether concentration, and revealed an overall 65% rate of infection with parasites considered at least potentially pathogenic. Included were Trichuris trichiura (34.3%), hookworm (5.5%), pathogenic (large race) Entamoeba histolytica (18.2%), and Giardia lamblia (6.9%). No human Ascaris was detected on Rongelap at that time; however, several spe- cles of non-pathogenic intestinal protozoa were identified. Not unexpectedly, trichuriasis was especially prevalent in the 6 to 20-year age group, which had an infection rate of 70.0%. Eosinophilia (>5%) was found in 67.8% of 109 individuals tested. Although anti-parasitic treatment of various kinds was given sporadically on an individual basis during subsequent years, no systematic attempt at island~wide treatment was made on Rongelap until 1977-8, when a broad-spectrum helminth eradication/suppression effort was undertaken. By that time it had become clear that roundworm (Ascaris) infection had been introduced and was a significant problem to the atoll inhabitants. A similar effort was made on . Utirik in 1978-9, but it was limited to the use of an agent known to be primarily ascaricidal. These efforts were made possible by generous donations of mebendazole (VermoxR) by Ortho Pharmaceuticals and of pyrantel pamoate (Antiminth®) by Roerig Division of Pfizer Pharmaceuticals. The sampling and treatment methods employed and the results obtained are described here. Although treatment was aimed only at intestinal helminths, some information regarding the prevalence of intestinal protozoa was also gathered. The latter data are presented insofar as they are available (since sampling methods best sulted for diagnosis of helminthic infection may be inadequate for identifying intestinal protozoa), and the results for the two atolls are compared. B. Methods Because donations of anthelminthics were obtained at different times, the sampling/treatment schedules on the two atolls were not concurrent. Treat- ment with mebendazole on Rongelap began after an initial stool sampling in June 1977. Treatment with pyrantel pamoate on Utirik began after a first *Supported in part by Division of Hospitals and Clinics Grant ORL 79-01-77, Bureau of Medical Services, HSA, U.S. Public Health Service, DHEW. Carried out by W.A. Krotoski (Tropical Infectious Disease Research Program, Clinical ‘Research Dept., USPHS Hospital, New Orleans, LA 70118), F.B. Cogswell (Dept. of Tropical Medicine, School of Public Health and Tropical Medicine, Tulane U., New Orleans, LA 70112), and K.D. Knudsen, R.A. Conard, mem vu ew uo cil ~~ (Brookhaven National Laboratory, Upton, NY 11973). - 3% - and H.S. Pratt