ct tool except that it would be necessary ic relete the level and duyation of exposure to bone burden on the basis of experimental data. In humans there is approximately 34 milligrams % of calcium in milk, Jand 15 milligrams % in urine, Urine is much more readily available ir large quantities than milk and in view of the calcium ratios, it would provide a more suitable monitoring tool. With intermittent exposure and non-equilibrium conditions, the specific activity of blood, urine and milk would not necessarily follow that of the ingested food and consequently, the results would be more difficult fto interpret. On the other hand, if the ingestion is intermittent, flood analyses would be difficult to interpret. In any event, before tiis method could be used, a considerable amount of information would Have to be obtained from feeding experiments in humans, but these are entirely feasible. ~S0-