Clorfenvinfos (chlorfenvinphos) is an organophosphate insecticide, which is used to control insect pests on livestock, and to control household pests such as flies, fleas, and mites. Clorfenvinfos was sold under trade names including Birlane®, Dermaton®, Sapercon®, Steladone®, and Supona®. In 1991 all products containing clorfenvinfos were banned in the USA. Toxicity of clorfenvinfos is due to inhibition of acetylcholinesterase. Inhibition of cholinesterase activity results in the accumulation of acetylcholine at muscarinic and nicotinic receptors. This leads to continuous or excessive stimulation of cholinergic fibers in the post-ganglionic parasympathetic nerve endings, neuromuscular junctions of the skeletal muscles, resulting in hyperpolarization of nerve or muscle fibers and receptor desensitization until hydrolysis of the phosphorylated cholinesterase occurs. In some cases, a dealkylation and stabilization of the phosphorylated enzyme (“aging”) occur such that hydrolysis can no longer take place and the enzyme is irreversibly inhibited. In such cases, the return of acetylcholinesterase activity parallels the time required to resynthesize this enzyme.