Amounts of F/sup 18/ sufficient to permit studies up to 10 hours duration in domestic animals with non-toxic levels of total fluorine have become available from cyclotron production. The initial rate of disappearance of intravenously injected F/sup 18/ from the blood was found to be 41 and 32% of the dose/min. for the lamb and a mature cow, respectively. The over-all disappearance curve was resolved into 4 components, similar to comparable curves reported for calcium 45. Data from both sheep and cow experiments showed that absorption was rapid, probably occurring from the rumen. Generally, about 1% of the ingested dose represented the peak blood value which occurred at about 2 and 5 hours in the sheep and cow, respectively. The selective localization of F/sup 10/ in the skeleton appeared to be similar to that of calcium as judged from bone and mandible autoradiograms. It was shown that some of the ingested F/sup 18/ was deposited in various parts of the hen's egg and in cow's milk. 13 references, 5 figures, 3 tables.