experimental calves. Based on the very low, essentially background, plutonium concentrations in the control animal tissues, any unintentional plutonium exposure to the calves was shown to be minimal. Results from the Phase I calf tissue, along with results from past plutonium investigations, suggested that the variety of calf tissues collected during the definitive study (Phase II) could be reduced without compromising the validity of comparisons between the tn vivo and tn vitro plutonium-labeled treatments. Extrapolations to a percentage of dose retained per kg of organ are presented in Table 7. Exprapolated calculations, especially from very low concentrations, can sometimes obscure variability and, in other instances, result in significant retention figures which were unfortunately based on concentrations approaching the lower limit of detectability for direct counting. Final results from the two phases will be based on radiochemical analysis and will be significantly more valid. Phase II The transport of plutonium to milk, urine, and feces of the four adult cows is shown in Table 8. An average of 1.5, 2.4, and 2.2 percent of the intravenous dose was transported to milk, urine, and feces, respectively, during the first 120 hours after injection. those observed in Phase I. Many samples, These transport values are basically similar to including all calf tissues, quality control assays on both the tn vivo and tn vitro plutonium-labeled milk, and some blood samples, still require final analysis. Most of these remaining samples have been screened for plutonium activity with the phoswich system, but many will also be analyzed using radiochemical techniques. A subsequent report will include the significant findings from both Phase I and Phase II. 199