Thyroxine is the main hormone produced by the thyroid gland. The thyroid hormones, triiodothyronine (T3) and thyroxine (T4), are tyrosine-based hormones produced by the thyroid gland that are primarily responsible for regulation of metabolism. Iodine is necessary for the production of T3 and T4. A deficiency of iodine leads to decreased production of T3 and T4, enlarges the thyroid tissue and will cause the disease known as goitre. T4 is one of the major thyroid hormones and are primarily responsible for regulation of metabolism. Our Thyroxine (T4) Immunoassay kit is species independent and designed to quantitatively measure T4 present in serum, plasma, urine, extracted dried fecal samples, and tissue culture media samples.