Almost all individuals tested were over 15 years of age. Fluorescent immunoassays were performed by the Parasitic Diseases Branch of the Centers for Disease Control, Atlanta, Georgia. The overall prevalence of positive titers was 93.6%, a finding to be expected on the basis of comparison groups (p <0.05). The MLTsof the four groups were similar, however, whentiters <4 were excluded, suggesting that if infection did occur there waslittle, if any, difference in ability to mount an antibody response. Table 3b shows that individuals living on Rongelap had including Oceania.”* A greater numberofpersons with insignificant titers (<4) was found in the Rongelap and Ailingnae groups (Table 3a). Furthermore, the mean log titer (MLT) of the combined Rongelap and Ailingnae groups was significantly lower than those of the Utirik and sons from Rongelap and Ailingnae were included, although the differenceis not statistically significant. It is possible, therefore, that the lower mean toxoplasma antibodytiter of the Rongelap-Ailingnae exposure group wasdue to a decreased opportunity for exposure to the investigations by others in tropical regions, the lowest MLTs whether or not exposed per- Table 3 Serum toxoplasmatiters and chorioretinal scars. a) Rongelap and Ailingnae Utinik Comparison 6.6643.72 8.29+2.49 7.8142.49 (61)** (97) (100) 18.0% 3.1% 4.0% 8.12+2.19 8.55+2.03 8.14+1.95 MLT* <4 MLT minus <4 b) MLT MLT minus Rongelap and - Ailingnae Exposed Exposure Group Island of Residence Ebeye Majuro Rongelap Utirik 7,.69+2.51 (103) 8.11243.34 (62 7.22+3.23 (87) 8.48+2.56 (172) 7.844+2.44 (69) 8.57+2.64 (53) 7,624+2.84 (71) 8.49+2.36 (172) c) Age Distribution <10 yr 10-19 yr >19 yr Rongelap and Ailingnae 5.89+3.55 (28) 8.2743.58 (11) 6.82+3.88 (22) Utirik 8.36+3.00 (50) 7,86+1.83 (14) 8.3641 .82 (33) Comparison 7.49+2.56 (39) 7.76+2.80 (21) 8.15+2.26 (40) me t 2 3 3 J Jo o« au