2,3-Butanedione monoxime, also known as diacetyl monoxime, is a nucleophilic agent which dephosphorylates acetylcholinesterase poisoned with organophosphates. This "chemical phosphatase" activity stimulated studies of the effect of 2,3-butanedione monoxime on phosphorylation-dependent cellular processes. As a result of these studies, we know that the drug affects a number of mechanisms including muscle contraction, ionic current flow and synaptic transmission. Furthermore, it may be used as a component of cardioplegic solutions since it protects cardiac tissue exposed to certain ischaemic conditions. While this MiniReview reveals the diversity of its cellular actions, there continues to be unresolved questions regarding its molecular mechanism.