In a radio receptor assay on the binding at the [3H]a-bungarotoxin binding site to the nicotinic acetylcholine receptor (nAChR) obtained from housefly and honeybee head membranes, nicotine, nornicotine, anabasine and dihydronicotyrine, all with highly basic nitrogen, had a strong binding affinity, whereas myosmine, nicotyrine and cotinine, with low basic nitrogen, did not. Structure-binding relationships of the above nicotinoids and pyridylmethylamines mostly coincided with the previously studied relationships to the insecticidal activity, the effect on nerve activity and the inhibition of acetylcholinesterase (AChE). Both enantiomers of nicotine had an affinity for nAChR, although the affinity was higher in the l-form than in the d-form. Imidacloprid interacted at the same site on the nAChR, but oxadiazolone, a potent ACNE inhibitor, had no affinity.