The accumulation of data from these surveysis becomingincreasingly 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 by this 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 calculations if desired. This report also contains a brief addendum on the vegetation of RongelapIsland. Summary of Past Findings Reports have been published on the findings of surveys madeat the following times after exposure: initial examination,’ 6 months,’ 1 year,’ 2 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. Depression of the peripheral blood elements as represented by mean population levels occurred as follows. Lymphocytes fell promptly and by the third day were about 55% of the control values in adults, and slightly 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 werestill found to be below the comparison population levels (75 to 80%). At 3 years the mean lymphocyte counts wereslightly below those of the comparison population. At 4 years the mean level appeared to be aboutthe, same as that of the comparison population, but many counts remained lower. sure, that the lymphocytes were considerably de- Neutrophil levels fluctuated considerably during the first few weeks butfell gradually to a low of about 50% of comparison population levels by the 6th week after exposure. Slow recovery ensued, but at 6 monthsthey werestill slightly below the unexposed levels. However, by 1 year post exposure they had returned to the level of the comparison population and have remainedso, 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 body dose of radiation and the beta irradiation of population but higher than at the 6-month survey. Although further increases were apparentat the years,’ 3 years,® and 4 years.® The following isa brief summaryofthe 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 lach- rymation and burningofthe eyes. Followingthis, the people remained asymptomatic until about 2 weeksafter the accident, when cutaneouslesions andloss of hair developed, due largely to betairradiation of the skin. It was apparent when the people werefirst examined, a few days after expo- pressed andthatsignificant doses of radiation had probably been received. In addition to the whole- 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 underthree headings according to the modeof exposure: penetrating irradiation, skin irradiation, and internal irradiation. platelet count wasstill below that of the control 2-, 3-, and 4-year examinations, the levels were still below those of the comparison population. Changesin hematocrit were not remarkable in any of the groups. Clinical examinationsrevealed no disease processes or symptoms which could beattributed to radiation effects, aside from skin lesions, loss of The changesin the peripheral! blood of the more heavily exposed Rongelap people whoreceived 175 r will be reviewed in the section on hemato- hair, and early symptoms. Epidemics of chicken pox and measles occurred. The diseases encountered were no moresevereorfrequentin the irradiated group than in the unexposed group, even during the period of greatest depression of peripheral blood elements. Three persons in the exposed and Appendices 1 and 2). The changes in the with a hypertensive heart disease which had been PENETRATING IRRADIATION logical examinations(see Figures 33, 35, and 38, population died of disease: (1) a 46-year-old man