reviously described and the bloods for leukocyte cultures were furnished taj David atcher. Of 20 patients studied by the serial sample technique, the incidenfe of ncreased anomalies is equivocal in those patients up to 10 millicure dose ange . ncrease is at the limit of significance in the doce range above 10 millicurfes. It hould be pointed out that these studies were based on a large series of biabd samples n each given patient rather than a "before" and "after" sample as has been feporte y others. Mr. Satcher is currently preparing his observations for publication. tudies of Peroxidase in Thyroid and Other Tissue Several years ago a study of peroxidase activity in thyroid tissue was bndertakey mnder this grant with the idea that it might prove to be another way to explire. adiation effect. Because at that time there was presumptive evidence that A peroxidase as present in thyroid tissue it was thought that this played some part in the onvergion of iodide to iodine am the iodination of organic compounds wi the hyroid. Ubservations previously described under this contmact suggested that one of the arly manifestations of radiation effect was a failure of the trapping mechahisn. An experimental method described by Neufeld et al. to measure peroxidasp had tilized the rate of oxidation of a leuco dye in thepresence of hydrogen pefoxide. he reaction mixture of hydrogen peroxide, phosphate citrate buffer and redupbed dye olution was used as a substrate mixture into which various samples of omogpniized issues were introduced. The rate of the reaction within the mixture was defermined by spectrophotametric method using a source of light with a wave length of 64f mi. Readings ere determined at 5 second intervals after the addition of the homogenate. [Catalase ctivity was inhibited by adding 2-4 dichlorophencl. A large variety of rat] tissues ere studied in addition to the thyroid. There was a wide range of peroxidagke activity ound in these tissues. As anticipated, the small intestine showed the largpstamount f peroxidase activity. The thyroid was about equivalent to the lung. Perokidase ctivity in the thyroids of many different animals was studied by this me on. | There as a considerable variation in the peroxidase activity in thyroids among vario1s pecies. Since it was suspected that the variation might be related to the §egree of ellularity in the thyroid, microscopic sections of the same tissues (fran w omogenates were made) were projected on large pieces of paper and tracings fade of the ells, colloid and connective tissue. The areas were cut out amd weighed tofdetermined he percentage of cells, connective tissue and colloid making up the tissue.] It was urprising to find that although the ratio of the volume of cells to the volime of colloid as very different among different species there was no true relationship befween the ell content of the tissue and the peroxidase activity among these species. The question arose whether the oxidative reaction being measured by thelleuco dye as actually related to the production of thyroid hormone and whether the pefoxidase ctivity might be under the influence of TSH. Accordingly, TSH was tested bbth in vivo nd in vitro. It was surprising to find that there was no significant diffefence etweentheoxidative activity of thyroids previously stimulated with TSH anf those which ere unstimulated. The effect of TSH on the thyroid was confirmed by the prgserce of yperplasia demonstrated in microscopic sections of the tissue used. In other studies the relationship of the peroxidase activity as measured by the euco dye method to the iodination of organic substances in physiological syftems was tudied. The basis for the reaction was the iodination of tyrosine. A reacfion