The acridine ring system is a basis for new fluorescent probes of known stereochemistry, for fundamental study of cholinergic neural transmission. Acridine, an aromatic heterocyclic ring, fits into the anionic cleft of acetylcholinesterase (E.C.3.1.1.7). The acridine ring system lends itself to the design and synthesis of spectroscopically active, new cholinergic system probes of known and well defined stereochemistry for study of the lateral and longitudinal dimensions of the anionic cleft, the stereochemistry of the esteratic subsite and the nature and location of the allosteric subsite in this enzyme. Stereochemically defined acridine system probes for AChE can subsequently be used for comparative studies of the stereochemistry and fundamental nature of cholinesterase (E.C.3.1.1.8) and cholinergic receptor(s). Acridine system probes adapt themselves to spectral and kinetic studies of their interaction with cholinergic systems. Analytical systems include NMR and fluorescence.