‘ a in Chapter III of reference (1). HEMATOLOGIC OBSERVATIONS It is generally considered that changes in the blood are the most sensitive biologic indices of exposure of living human beings to radiation. Accordingly ex tensive simple hematologic studies were performed on the Marshallese, Since there were no previous hematologic studies on the exposed Marshallese, it was necessary to set up control groups of non exposed Marshalled of the same age and sex distribution for comparative purposes. I shall restrict my comments to the findings in the group from Rongelap since the teaporal sequence of events are identical in all of the exposed groups. Of course the depression was less marked in the less severly exposed groups. Neutrophile Count The absolute neutrophile count of both the younger and older age groups fell during the second week to a value approximating 70 to 80% of that of the controls, Following the depression there was an oscillation roughly around the control value until about the 30th post exocsure day at which time there was a progressive decrease in the blood count with minimum values being attained around the 45th day efter exposure. It is of interest, that thedepression in the children, less than 5 years of age was greater then in the individuals who were greater than 5 years of age. Following this maximal depression there was a slow return of the neutrophile counts towards normal. However at 6 months they were still depressed. years the neutrophile counts were back to the control level. At cne year and two However at 3 years there ves a drop in the absolute mean neutrophile count but this also occurred in the control population, It is not known whether lowered counts represent a popu- lation trend as has been noted in the Japanese for both irradiated and non irradiated populations, or wether it is merely a statistical fluctuation that is to be expected | in this type of study. “‘Lynwhocyte Count. More work is necessary on this point. IDOEARCHIVES