JNO The accumulation of data from these surveys is becoming increasingly voluminous. Since conditions have not been favorable for performance of extensive statistical analyses or use of electronic computing procedures to store and manipulate the data, the annual survey reports published bythis Laboratory are made as complete as possible. This report, therefore, includes a considerable amount of raw data, much of it in appendices, so that others may have an opportunity to make further calculationsif desired. Summaryof Past Findings Reports have been published onthefindings of surveys madeat the following times after expo- sure: initial examination,’ 6 months,’ 1 year,’ 2 years,’ 3 vears,’ 4 vears,” and 5 and 6 years.’ The following is a brief summaryof the findingspreviously reported. During the first 24 to 48 hr after exposure, about *% of the Rongelap people experienced anorexia and nausea, A few vomited and had diarrhea. Many also experienced itching and burning of the skin, and a few complainedof lachrymation and burning of the eyes. Followingthis, the people remained asymptomatic until about 2 weeksafter the accident, when cutaneouslesions and loss of hair developed, due largely to betairradiation of the skin. It was apparent when the people were first examined, a few days after expo- sure, that the !ymphocytes were considerably de- pressed and that significant doses of radiation had probably been received. In addition to the wholebody dose of radiation and the beta irradiation of the skin, radiochemical analyses of the urine showed that measurable amounts of radioactive material had also been absorbed internally. The effects of the radiation can best be summarized under three headings according to the modeof exposure: penetrating irradiation, skin irradiation, and internalirradiation. PENETRATING IRRADIATION The changesin the peripheral blood of the more heavily exposed Rongelap people who received 175 r will be reviewed in the section on hemato- logical examinations (see Figures 34, 39, and 43, and Appendices | and 2). The changes in the Ailingnae and Utirik groups were similar butless marked. Certain unexplained fluctuations have occurred from year to year in the peripheral blood levels of the comparison populations as well as of the exposed groups. The mean leukocyte level of the exposed group showed a marked decrease at the time of the 1960 survey (no unexposed people were examined). Depression of the peripheral blood elements as represented by mean population levels occurred as follows. Lymphocytesfell promptly and by the third day were about 59%of the control values in adults, andslightly lower in children. There was only slight recovery after six months. At 2 years, although further recovery was evident, the mean values of these cells were stil! found to be below the comparison population levels (75 to 80%). At 3 years the mean lymphocyte counts wereslightlv below those of the comparison population. At + years the mean level appeared to be about the same as that of the comparison population, but many counts remained lower. However,at 5 years, lymphocyte levels appeared for thefirst time to equal those of the unexposed group, except that analyses. showed more counts below the average of the unexposed group. Neutrophil levels fluctuated considerably during the first few weeks but fell gradually to a low of about 50% of comparison populationlevels by the 6th week after exposure. Slow recoveryensued, but at 6 monthsthey werestill slightly below the unexposed levels. However, by | year post ex- posure they had returned to the level of the comparison population and have remained so, with the possible exception of those of children < 12 years old, which generally have been lower than those of the unexposed children of comparable age. Platelets fell to about 30% of the unexposed values by the 4th week. By 6 months they had reached 75% of the controls; at 1 year the mean platelet count wasstill below that of the control population but higher than at the 6-month survey. Although further increases were apparentat the 2-, 3-, and 4-year examinations, the levels were still below those of the comparison population. At 5 years post exposure, exposed people sull had mean platelet levels 10 to 15% below those of the unexposed group. Changes in hematocrit were not remarkable in any of the groups during the period of maximum depression of leukocytes. However, it appeared