The accumufa¥fon of data from these surveys ts becoming increasingly voluminous. Since condi- tions 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 bvthis Labpratory are made as complete as possible. This report, therefore, includes a considerable amount of raw data, much ofit in appendices, so that others may have an opportunity to make further calculationsif desired. This report also contains a brief addendumon the vegetation of Rongelap Island. Summary of Past Findings Reports have been published on the findings of surveys made at the following times after exposure: initial examination,' 6 months,’ 1 year,’ 2 years,* 3 years,? and 4 years.* The following is a brief summary of the findings previously 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 complained of lachrymation and burning of the eyes. Following this. the people remained asymptomatic until about 2 weeks after the accident, when cutaneouslesions and loss of hair developed, due largely to beta irradiation of the skin. It was apparent when the people werefirst examined, a fewdaysafter exposure, that the lymphocytes were considerablydepressed 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 modeofexposure: penetrating irradiation, skin irradiation, and internal irradiation. 4, PENETRATING IRRADIATION The changes in the peripheral blood of the more heavily exposed Rongelap people who received 175 r will be reviewed in the section on hematological examinations (see Figures 33, 35, and 38, and Appendices | and 2) The changes in the Ailingnae and Utirik groups were similar but less marked. Certain unexplained fluctuations have occurred from vear to year in the peripheral blood levels of the comparison populations as well as of the exposed groups. Depression of the peripheral blood elements as represented by mean population levels occurred as follows. Lymphoevtes fell promptly and bythe third day were about 35% of the control values in adults, and slightly tower in children. There was only sight recovery after six months. At 2 years, although further recovery was evident, the mean values of these cells were still found to be below the comparison population levels (75 to 80°). At 3 years the mean Ivmphocyte counts wereslightly below those of the comparison population. At 4 years the mean level appeared to be about the same as that of the comparison population, but manycounts remained lower. Neutrophil levels fluctuated considerably during the first few weeks but fell gradually to a tow of about 50% of comparison population levels by the 5th week after exposure. Slow recovery ensued, but at 6 monthsthey werestill slightly below the unexposed levels. However, by | year post exposure 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 70% 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 apparent at the 2-. 3-, and 4-year examinations, the levels were still below those of the comparison population. Changes in hematocrit were not remarkable in anyof the groups. Clinical examinations revealed no disease processes or symptoms which could be attributed to raciiation effects, aside from skin lesions, loss of hair, and early symptoms. Epidemics of chicken pox and measles occurred. The diseases encountered were no moresevere or frequent in the irradiated group than in the unexposed group, even during the period of greatest depression of periphera: blood elements. Three persons in the exposed population died of disease: (1) a 46-year-old man with a hypertensive heart disease which had been