Abstract: A polarization fluoroimmunoassay for T.sub.3 or T.sub.4 thyroid hormones where a serum sample is assayed by contacting the sample with a base to denature the thyroxine binding globulins and thereby form a solution, incubating the solution, contacting the solution with a separating agent and separating bound thyroid hormone from the serum, contacting the separating agent with bound thyroid hormone with an antibody against the thyroid hormone, incubating the separating agent-antibody combination, separating free antibody and thyroid hormone bound antibody from the separating agent, contacting the free antibody with fluorescent labelled thyroid hormone and measuring the fluorescence polarization as an indication of the thyroid hormone in the sample.

Abstract: A T.sub.3 uptake polarization fluoroimmunoassay where a sample is assayed by contacting a serum sample with T.sub.3 to form a solution, contacting the solution with a separating agent and incubating the same, separating T.sub.3 bound to the separating agent from the serum sample, contacting the T.sub.3 bound to the separating agent with an antibody against T.sub.3, incubating and separating the agent-anti-body combination, separating free anti-body and contacting the free antibody with fluorescent labeled T.sub.3 and fluorometrically measuring the fluorescence polarization.