Preparation of 125I-thyroxine and 125I-triiodothyronine of high specific activity for the radioimmunoassay of serum total T4 and T3.

A simple and inexpensive procedure for the preparation of high specific activity 125I radioiodinated triiodothyronine and thyroxine is described. The specific activities achieved are approximately 350 Ci/g for 125I-T4, and either 200 Ci/g for 125I-T3 depending on the reagents employed. The high specific activity 125I-T4 and 125I-T3 are suitable for the routine radioimmunoassay of serum total T3 and T4. When properly stored they have a self life of at least seven weeks.