Sulfotransferase family cytosolic 1B member 1, also known as Sulfotransferase 1B1, Sulfotransferase 1B2, Thyroid hormone sulfotransferase, SULT1B1 and ST1B2, is a cytoplasm protein that belongs to the sulfotransferase 1 family. Sulfotransferase enzymes catalyze the sulfate conjugation of many hormones, neurotransmitters, drugs, and xenobiotic compounds. These cytosolic enzymes are different in their tissue distributions and substrate specificities. SULT1B1 is highly expressed in the liver, peripheral blood leukocytes, colon (mucosal lining), small intestine (jejunum) and spleen. A lesser expression of SULT1B1 was observed in the lung, placenta and thymus. SULT1B1 catalyzes the sulfate conjugation of many hormones, neurotransmitters, drugs and xenobiotic compounds. Sulfonation increases the water solubility of most compounds, and therefore their renal excretion, but it can also result in bioactivation to form active metabolites. SULT1B1 sulfates dopamine, small phenols such as 1-naphthol and p-nitrophenol and thyroid hormones, including 3,3'-diiodothyronine, triidothyronine, reverse triiodothyronine and thyroxine.