Conformational and geometrical properties of the hexamethylenebis(trimethylammonium) (CH3)3N+-(CH2)6)-N+(CH3)3 (hexamethonium) and its derivatives with various degree of conformational flexibility of interonion chain having disulfide or two dimethylsilane groups or difluoromethylene chain instead of cholinesterase reversible inhibitors have been determined using molecular mechanics methods. Conformation-activity relationships between these inhibitors and different cholinesterases (human erythrocyte acetylcholinesterase, horse plasma butyrylcholinesterase, cholinesterase from the brain of the grass frog Rana temporaria and optical ganglia from the Pacific squid Todarodes pacificus and Comandor squids Berryteuthis magister from various areas) were investigated. Hypothesis of complex influence of conformational and geometrical properties (if molecules on anticholinesterase efficiency of compounds under investigation was formulated.