Publisher Summary Insects have provided material well suited to the investigation of CNS acetylcholine receptors. The central nervous tissues of these organisms have proved amenable to both radiolabelled- ligand-binding studies and single-cell electrophysiology of identifiable neurones. Binding studies have resulted in the characterization in vitro of three putative acetylcholine recognition sites each with a distinct pharmacological specificity. Of these three putative acetylcholine receptors defined biochemically, the α-bungarotoxin-sensitive receptor has been investigated the most. Pharmacological differences have emerged between this insect receptor and the nicotinic receptor of vertebrate muscle and electroplax tissue. The insect receptor is, for example, much less sensitive to decamethonium and carbamylcholine. Also the receptors mediating cercal-afferent, giantinterneurone synaptic transmission are much more sensitive to α-bungarotoxin and less sensitive to hexamethonium than the nicotinic receptors of vertebrate autonomic ganglia. Two other putative insect acetylcholine receptors both of which are insensitive to α-bungarotoxin have been investigated by radiolabelled-ligand binding methods. Insect material is particularly well suited for developmental and genetic approaches to receptor biology. Genetic studies offer another approach to the study of receptor biology for which insect material is supremely well suited. Hereditary changes in acetylcholine receptor structure have been reported in nicotine-resistant strains of Drosophila melanogaster.