effect of thyroidectomy of immature male chickens on circulating thyroid hormones and on response to thyroidstimulating hormone and chronic cold exposure previous studies in the authors laboratory established that thyroidectomized tx immature male chickens had significant levels of circulating thyroid hormones and it was proposed that extrathyroidal tissue might be present three experiments were conducted to further investigate this possibility in all experiments thyroid glands were removed surgically at 3 wk of age in the first experiment birds were kept until 20 wk of age it was found that only triidothyronine levels were reduced significantly in the tx birds in the second experiment tx as well as shamoperated control groups received a single iv injection of bovine thyroidstimulating hormone tsh to determine if extrathyroidal tissue in tx birds would respond to exogenous tsh it was found that circulating thyroxine t4 concentrations in shamoperated control birds but not tx birds were increased following tsh injection in the third experiment tx and shamoperated birds were exposed chronically to cold 7 c and only circulating t4 was found to be elevated in both groups it was concluded that extrathyroidal tissue in tx birds does not respond to tsh