All equilibrium conformations of 12 anti-acetylcholinesterase organophosphorus inhibitors were calculated by the molecular mechanics method. The accessibility of the phosphorus atom of the inhibitors for interactions with the nucleophilic group at the enzyme active centre was estimated. The conformers with the phosphorus atom sterically accessible from the side opposite to the breaking ester bond were classified as productive. A correlation was revealed between the activity of the inhibitors and the population of their productive conformation.