urine, feces, etc.) and the administered dose, "spiked" samples of each type were prepared in triplicate and assayed. These "spiked'"' samples were also recounted after a period of time to determine any time-related variations due In many cases, multiple samples were to the settling out of sample material. Tissue samples were not homogenized, but selected collected for analysis. samples were counted twice (top-bottom rotation). The variability between these two tissue counts will be used in the overall assessment of those uncer- tainties not associated with counting hardware and counting duration. Selected samples (primarily of low plutonium concentrations) are also being prepared for analyses by another laboratory which will employ more sensitive assay techniques. RESULTS AND DISCUSSION In this report, Phases I and II have been discussed separately in order to emphasize the experimental approach and to sequentially present some of the resulting data. Phase I The total plutonium transported to milk during the first 72 hours following intravenous plutonium injections was essentially one percent of the administered dose (Tables 4 and 5). At 72 hours post-injection, 1.3 and 0.81 percent of the dose had been secreted in milk for the first and second cows, respectively. While the percentage per kg of milk was definitely higher for the first cow (83 mCi dose) at hour 72, the basic secretion pattern was, as expected, quite similar between animals. The percentage of plutonium transported to urine was also similar, but the fecal excretion of plutonium did reveal differences between the two treatments. It should be noted, however, that the first cow developed a problem, apparently digestive in nature, and was not consuming a normal amount of feed. Consequently, the gross amount of fecal material had decreased sharply by the third collection day (0.8 kg for Day 3). Following multiple plutonium injections to the second animal, milk collections were fed to two calves. The dosing sequence and the respective amounts of plutonium ingested by each calf are shown in Table 6. and 153 uCi, Oral doses of 174 uCi ingested over the six-day dosing period, resulted in detectable plutonium concentrations for some calf tissues (Table 7). Several tissues collected at the calf sacrifice have been omitted from this table due to their low plutonium concentrations. Samples of muscle, gonads, thyroid, thymus, and blood were of limited value having very low nuclide concentrations. Two additional calves were used as control animals during the study to evaluate potential cross contamination. One was located inside the metabolism room, while a second control calf was housed in an outdoor pen completely removed from the experimental operation. The calf inside the metabolism room was, of course, the primary control animal and received identical handling as the experimental calves, i.e., it received milk at the same time as did the experi- mental animals and it was maintained in a metabolism stall between the two 186