the limiting factor was the potential external whole body exposure. It is now recognized that there can be situations where the fodine-131 exposure can be more limiting. An example of this was the Smalilboy surface shot on July 14, 1962 at the Nevada Test Site. The detonation was large enough to produce significant quantities of iodine-131 and yet of low enough energy yield so that the activity was not swept to high altitudes as usual, to be carried, away, diffused and diluted. The Data The highest value of fodine-131 measured in milk by the Public Health Service national network at any time was at St. Louis, Missouri for the period of August 1957 through July 195811. The calculated average dose was 1.5 roentgens to infants’ thyroidsa based on the usual assumption of drinking one liter of milk per day - the dose to an adult thyroid would be only about 1/10 as much. The next highest cal- culated total average dose was. 0.69 roentgens at Palmer, Alaska (October 1961 through September 1962) and the third highest was 0.63 roentgens for Salt Lake City, Utah (September 1961 through August 1962). Because of the unevenness of the iodine deposition near the Nevada Test Site it is possible that smail iocal areas could show values 10 times or so greater than the average for the general region. It is also probable that higher levels of iodine-131 existed in local areas around the Nevada Test Site during periods of heavy testing in the 1950s. The estimated doses to the thyroid given above involve some uncertainties in their determination but are based on some observed iodine-131 15. 20