after the accident. In addition, fallout duration and fallout arrival estimates derived from BRAVO fallout studies were in agreement with the observed fallout duration and arrival times. Our estimates of surface activity were transformed into estimates of surface exposure and exposure rate on an individual nuclide basis. The measured exposure and exposure-rate results reported in the literature were used to develop surface activity at locations and times of interest. Once the surface activity was derived, the intake pathway and estimate of intake were evaluated using the average I excreted by Rongelap adults for normalization. Estimates of thyroid absorbed dose, age at exposure, and intake of specific nuclides were tabulated for each location. For an adult male, the thyroid absorbed dose from iodine and tellurium radionuclides was 7.7 times the absorbed dose from !3!1 at Rongelap, 10 times that at Sifo Island, and 4.7 times that at Utirik Island. James, in an earlier attempt to estimate thyroid absorbed dose based on 1311 in urine, assumed the total dose was 2.6 times the dose from 13ly (Ja64). The factor 2.6 would be appropriate for slightly older fallout than that experienced at Rongelap, Utirik, and Sifo Islands. Our estimate of thyroid absorbed dose was based on ingestion intake. Inhalation intake and absorption through skin could not be reconciled with measurements of 131] in urine or with external exposure-rate measurements. The average and maximum estimates of total absorbed dose to the thyroid were derived. Observations of the range of 137¢8 body burdens during protracted exposure (Mi79) and Eve's estimate of the range associated with the contents of the stomach in cases of sudden death (Ev66) were used to estimate maximum thyroid absorbed dose. The maximum was estimated to be four times the average. The average internal thyroid dose at Rongelap Island was based on the average ly activity collected in urine. The contribution to thyroid dose from external sources was estimated from the air exposure caused by the decay of 142 nuclides making up the fallout composition. The external doses were similar to original estimates by Sondhaus for persons exposed at Rongelap and Utirik Islands, 1.75 gray and 0.14 gray (175 rad and 14 rad), respectively, which were derived from survey instrument readings taken at evacuation and film badge data from a nearby military outpost (S055). The external dose estimated for people at Sifo Island, 1.1 gray (110 rad), was greater than the 0.69 gray (69 rad) estimated originally from post-evacuation surveys of exposure rate. The difference was due to the presence of very short-lived activation and transuranic nuclides which, according to the nuclide composition, must have been present during exposure at Sifo Island. Medical observations concerning thyroid abnormalities have been tabulated along with the new thyroid dose estimated for each person. From these results, the mean cancer risk rate in the exposed population of 251 people was 150 thyroid cancers per million person-gray-years at risk (1.5 + 2.3 thyroid cancers per million person-rad-years at risk). The mean time at risk for thyroid cancer was 19 years. The mean thyroid nodule risk rate was 830 nodules per million person-gray-years at risk (8.3 + 12 per million person-rad-years at risk). The mean time at risk for a thyroid nodule was 18 years. ~ xiv -