key value for assessment of any current or projected situation for any particular isotope is the so-called Maximum Permissible Concentration or MPC. For strontiwn-90 this is the maintained concentration which is pelieved to be one-tenth of the minimal amount necessary to cause cancer in an adult. Recent Project SUNSHINE enalyses indicate that human bone specimens are approaching 0.001 of the MPC. Following the CASTLE series of shots, iodine-131 was identified.in the urine of the Marshallese natives, Service personnel, in the area, and e small number of individvals in the United States, but was maintained for only a short period of tine. GB The long-term strontium-90 hazard from air burst nuclear weapons depends upon a world-wide distribution of the contaminant. It appears likely that the number of nuclear detonations, whether air or surface, required to cause a world-wide long-term strontium-90 hazard would be so large as to result in devastation of much of the habitable world area. from the immediate destructive effects of the weapons. In such a case it is likely that any long-term effects on the population remaining would be of secondary importance. 132