Abstract: The comparison and evaluation of three RIA kits with different kind of separation reagents—T_4 (PEG), T_4 (M) and T_4 (ms) for the sensitivity, intraassay coefficient of variation, interassay coefficient of variation, stability, quality control diagram, normal value and correlation of T_4 (M) or T_4 (ms) to T_4(PEG) are described. The composition and operation of these RIA kits are simple. They have high sensitivity and stability, T_4 (M) and T_4 (ms) are highly correlation to T_4 (PEG). The NSB of T_4 (M) or T_4 (ms) is very low. These kits are advanced RIA kits in our country.