Abstract
The parameters of the isotopic exchange reaction between nonradioactive thyroxine or tniiodothyronine dissolved in ethyl alcohol with radioiodine extracted in ether were investigated. The effect of the concentration of carrier iodine on the yield of labeling as well as the different factors leading to its formation are discussed. A radiochemical yield of 95% /sup 131/I-thyroxine is obtained within 10-15.min. The method is very simple and favorable for very short-lived radioiodines. (auth)