The plutonium-238, -239, americium-241, and uranium values reported in the gonad, muscle, liver, lung, and femur samples collected from each animal are listed in Table 2. Duplicate samples were collected of the muscle, liver, and femur of animals numbers 13 and 15 and are also shown in Table 2. Comparison of the values for the two groups of cattle (three aged cows and two yearling bulls) reveals no major differences in concentrations, with the possible exception of plutonium in the femurs (see Fig. 1) which appears to be slightly higher in the younger animals. If this difference is real, it may be because of the more rapid growth rate of the bones of young animals, resulting in increased incorporation of plutonium in the bone. Also, as these animals were born within the area, they received a certain contribution from their dams prior to birth. More information relative to these observations will become available when data from the animals sacrificed in January, 1976, are obtained. On the basis of these five animals, there appears to be little difference in actinide concentrations between male and female gonads. The male gonads (~ 500 g wet weight) should certainly provide adequate ash for analysis. At present, the only comparable group of cattle for which gonadal data are avail- able is from the Rocky Flats area of Colorado where five aged cows and five yearling heifers were sampled in November, 1973, (Smith and Black, 1975). Values from these animals are compared to those reported from the Area 13 cattle in the following discussion and are displayed graphically in Figs. 2 and 3. As shown in Fig. 2, the median plutonium-239 concentration in the gonads from Area 13 cattle was approximately 25 times higher than that found in muscle. An even greater median concentration variation was found between these two tissues in the Rocky Flats cattle. The plutonium-239 median concentration in the gonads from the Area 13 cattle was approximately equal to that of the femurs and one-half to one-third that of liver and lungs. The concentrations in gonads of Rocky Flats cattle were higher than those in muscle, lung, liver, and femur. However, the concentrations in these tissues were generally less than those reported for similar tissues for Area 13 cattle. As shown in Fig. 3, the uranium concentration in gonads of Area 13 cattle was about ten times the median concentration in the other four tissue types. This increased concentration of uranium in the gonads was observed in the Rocky Flats cattle, also shown in Fig. 3. The median plutonium-238 concentration in gonads from Area 13 cattle was approximately equal to that in lung, liver, and femur tissues and approximately 100 times greater than that reported in muscle tissue. The americium-241 concentration in gonads of the Area 13 cattle was approximately equal to that of the liver and lung tissues, but twice as great as reported in the femur and approximately 50 times that found in the muscle. As shown in Fig. 4, the plutonium-239/americium-241 ratios were calculated for the five tissues from the two herds. These ratios were similar for both locations, but generally a smaller range of variation in concentrations was found in tissues from Area 13. 142