Abstract: Methods employing thyroid analog conjugates to enzymes and to immunogenic carriers are provided, which find use in the determination of thyroid compounds normally in physiological fluids, such as serum. The immunogenic carrier conjugates are used to raise antibodies specific to thyroid compounds. The antibodies and enzyme conjugates are used in assays for thyroid compounds. The thyroid analogs are characterized by the presence of only one phenyl ring that contains a hydroxyl substituent and one or two substituents in an ortho relationship to the hydroxyl substituent on the phenyl ring wherein the phenyl ring is conjugated to an enzyme or an immunogenic carrier by a bond or a linking group. Kits for conducting the methods of the present invention are also disclosed.