3. Lymphocytes. By the third day after exposure the mean lympho- cyte level had fallen to about 55% in the adults and 25% in the children of the unexposed comparison population. (Figure 1). The levels remained low Jonger than the neutrophiles and have been very slow in recovering. There was little recovery by 6 months Dut an upward trend has since occurred. After 3 years the lymphocytes were slightly below the mean level of the com parison population for all age groups and distributional studies of individual counts showed more lower counts in the exposed groupa. The 4 year study showed the highest level thus far attained (3600 cells/mm® compared to 3700 cells/nm in the unexposed people) and recovery of this blood elenent is considered almost complete. However, a scattergram of the individual counts plotted according to age and accumulative distribution curves showed more of the counts to be lower than in the unexposed population. 4. Platelets. There was a steady reduction in the platelets in the peripheral blood after exposure reaching a low of about 30% of the un~ exposed group by the fourth week. (See Figure 2). A rapid recovery trend was then followed by a fluctuating, slow recovery pattern, the males show ing slower recovery than the females. Bven at 4 years post-exposure the platelet procuction does not appear to have recovered completely. The counts were higher than a year ago but compared with mean unexposed levels were about 12% lower in the males (greater than 10 years of age) and 9% lower in the females. A scattergram (Figure 3) shows individual counts in the maleg and the mean curve of the controls plotted against age. ponderantly below the control curve. The counts are pree- This trend is not as marked in the females, 53. Eosinophiles and monocytes showed depression and recovery roughly paralleling the neutrophiles. Studied. Bosinophilia is present in all the populations During the past survey the differential counts showed eosinophilia =o