diffused and diluted as had occurred for larger bursts in the atmosphere. a 2, ; 3 The Data The highest annual average value of iodine 131 measured in milk by the Public Health Service national network(fig. 5) at any time was at St. Louis, Mo., for the period of August 1957 through July 19584 The calculated average dose was 1.5 FIGURE 5.~—U.S. Public Health Service National Milk Network. A San Juan, Puerto Rico A Honolulu, Hawaii A Palmer, Alaska roentgens to infants’ thyroids based on the usual assumption of each drinking one liter of milk per day -—the dose to an adult thyroid would be only about %10 as much. The next highest calculated total average dose was 0.69 roentgen at Palmer, Alaska (October 1961 through September 1962), and the third highest was 0.63 roentgen for Salt Lake City, Utah (September 1961 through August 1962). Because of the unevennessof the iodine deposition near the Nevada Test Site it is possible that small local areas might show values 10 times or so greater than the average for the general region. It is also probable that higher levels of iodine 131 than these existed in local areas around the Nevada Test Site during periods of heavy testing in the 1950s. The above estimated doses to the thyroid involve some uncertainties in their determination but are based on some observed iodine 131 levels in milk samples. Theoretical calculations of thyroid doses have been attempted, based on other types of radiation monitoring such as collection of radioactive particulates in the air or measurements of radiation at three feet above the ground from deposited fallout. To date, all of these methods suffer severe uncertainties. These monitoring procedures, equipment and data are useful for the purposes for which they were intended. Thedifficulty is in attempting to use one type to predict another in a quantitative way. Evaluation All of the above calculated thyroid radiation doses may be placed in perspective by reference to quoting from a National Academy of Sciences report." In describing the therapeutic use of iodine 131 in the treatment of hyperthyroidism, the report stated: “.. There is no evidence at hand, except for one doubtful case in a child, that any of the treatments for hyperthyroidism has produced a thyroid cancer, although doses have ranged from a few thousand rad (roentgens) upward .. .” There can be circumstances wherelevels of iodine 131 in milk can be a more controlling factor than external gamma expo- 12 13