(±)-quinuclidinyl benzilate (3-quinuclidinyl benzilate), is a specific muscarinic cholinergic receptor antagonist. It binds potently but reversibly to the muscarinic cholinergic receptors of mammalian brain and peripheral tissues. 3-quinuclidinyl benzilate was invented by Hoffmann-La Roche Inc in 1951, while investigating antispasmodic agents resembling tropine for the treatment of gastrointestinal conditions. In the 1960s 3-quinuclidinyl benzilate, was developed and weaponized as a new chemical agent for battlefield use as a psychochemical. Assigned the NATO code BZ it is classified as a hallucinogenic chemical warfare agent that affects both the peripheral and central nervous systems (CNS). It is one of the most potent anticholinergic psychomimetics known, with only small doses necessary to produce incapacitation. The primary route of absorption is through the respiratory system but absorption also can occur through the skin or gastrointestinal tract. BZ is odorless and is usually disseminated as an aerosol. Data regarding the health effects of BZ in humans following inhalation exposure are limited to military application studies. Pharmacologic activity of 3-quinuclidinyl benzilate is similar to other anticholinergic drugs (eg, atropine) but with a much longer duration of action. It was shown that I[3H]-3-quinuclidinyl benzilate accumulated in various brain regions after intravenous injection. The specific binding of [3-3H]3-quinuclidinyl-benzilate and [125I]3-quinuclidinyl-(3-iodo-4-hydroxy-benzilate) to rat brain subcellular fractions is parallel in myelin, synaptic plasma membrane and mitochondrial fractions with a 3-4-fold enrichment observed in synaptic plasma membrane over crude mitochondrial fractions. These findings suggested the use of 3-quinuclidinyl benzilate as a binding probe useful in assaying low levels of muscarinic receptor in tissue culture and other biological sources including labeling the receptor in vivo for autoradiographic studies. M2 muscarinic acetylcholine receptor (M2 receptor), essential for the physiologic control of cardiovascular function through activation of G protein-coupled inwardly-rectifying potassium channels, was shown to bind 3-quinuclidinyl benzilate with high affinity in vitro.