Antimony (Sb) is a semimetal element of Group V, sharing some chemical properties with lead, arsenic, and bismuth. The most stable valence states of antimony are Sb(3+) and Sb(5+). Numerous inorganic and organic compounds of antimony are known. Most of the common antimony compounds are slightly to readily soluble in water. Antimony is thought to exert its toxic effects by interacting with intracellular enzymes or cofactors. A number of sulfhydryl-containing compounds reduce the toxic effects of antimony, suggesting that it may bind to cellular sulfhydryl groups. Antimony has been reported to increase the activity of heme oxygenase, to increase the action of thyroid hormone, and to decrease the toxicity of selenium, but the mechanisms of these effects are not known. Antimony has been found to be mutagenic in several test systems, and various types of tumors, including lung neoplasms, have been induced in rats upon inhalation exposure; however, no evidence has been found that orally ingested antimony is carcinogenic.