318 ADAMS ET AL. 3, x? = 0.759. P = 0.86) (Table 2). Persons 27 years of age or younger were excluded from this particular analysis because the youngest exposed individuals were 28 years old in 1982. Since there was no apparent effect of radiation exposure on the prevalence of retinochoroiditis, the combined prevalence for all groups was calculated and found to be 3.9%. The age-specific prevalence of retinochoroiditis in seropositive persons wasrelatively constant between the ages of 10 and 59 years. Based on the discovery of three new cases of retinochoroiditis in 275 seropositive adults reexamined after 4 years, the incidence was 273 cases/ 100.000 seropositive adults per year. DISCUSSION The high prevalence of antibody to T. gondii frequently found among other Pacific populations*’ is also present in the Republic of the Marshall Islands. Large local variations in the frequency of positive serologic tests for T. gondii were not detected when analyzed according to age, sex, or atoll of residence at the time of serologic testing. Frequent travel by the Marshallese amongthe atolls may explain the relative homogeneity of the infection. Furthermore,pigs, rats, and fowl are ubiquitous. However, cats, an important source of human infection on some Pacific islands,'' are currently uncommon on Rongelap and Utirik. Therefore othersignificant modes of infection may exist, such as ingestion of inadequately cooked cyst-containing meat. Local pork is not eaten frequently, but when it is prepared on festive occasions many persons might be exposedto a single source. Chorioretinopathy was found in 3.9% of 485 seropositive Marshallese. A prevalence of 11% was found in 192 persons examinedon Trukatoll in 1964.’ However, the Truk lesions were not felt to be typical of toxoplasmosis, despite the presence of Toxoplasma dye test antibodies in 80%of the surveyed population,andfilarial infection was considered as a possible etiology. Filariasis is not present on the low Marshallese atolls, but retinal lesions are clearly an important health problem. Repeat ophthalmologic examinations performed in 1985 on 275 seropositive persons who had normal eye examinations in 1981 revealed three previously undiagnosed cases of retinochoroiditis. The ages of the individuals were 40, 42, and 53 years. If these were in fact new Toxoplasmalesions, the resulting incidence of retinochoroiditis in seropositive persons would be 273 cases/year/ 100,000 persons. However. the late developmentofretinochoroiditis in the three individuals is not entirely consistent with the relatively stable age-specific distribution of ret- inochoroiditis shown in Table 2 nor the current view that ocular toxoplasmosis usually occurs prior to age 40.'? Of 28 personswith retinal lesions compatible with toxoplasmosis, 5 (18%) had significant visual loss in one or both eyes. With a population of 33,000, a seropositivity prevalence of 93.8% in those 10 years of age or older, a prevalence of retinochoroiditis of 3.9% in seropositive persons, and visual loss occurring in 18%of those with retinochoroiditis, one may estimate that as many as 200 visually impaired personsin the Republic of the Marshall Islands owetheir disability to toxoplasmosis. Thesefindings suggest that Toxoplasma epidemiology in the Republic of the Marshall Islands differs from that previously reported for other Pacific islands whereit was theorized that the ubiquityof early childhood infection made clinically significant toxoplasmosis andfetal infection unlikely.* It was cautioned, however, that clinically significant toxoplasmosis might become more common as sanitation practices improved. Against this background, antibody to T. gondii was assessed in a subpopulation of Marshallese accidentally exposed to radioactive fallout in 1954. The finding of significantly fewer positive titers for Toxoplasma antibodies amongthe people of Rongelap who received 110-190 rads of whole-body gammaradiation suggests that the relative infrequency of antibodyin this subgroup mayberelated to their high radiation exposure. However, mean antibody titers in seropositive persons in this group, even when analyzed by age, were similar to those in persons considered to have either a low radiation exposure (11 rads for the Utirik population) or none at all. The prevalence of seronegative individuals was in- creased in the Rongelap groupforall age categories. The prevalence of positive titers in the Rongelap group wassignificantly lower than that of unexposed adults currently living on Rongelap, a finding which does not support the conclusion that that island has provided less opportunity for acquiring toxoplasmosis than the other islands studied. Clinically there appears to be no evidence that toxoplasmosis has posed a greater problem for