Ensuing from the molecular orbital calculations after Kier(1969), it is evident that the molecular configurations of nicotine and acetylcholine have a quaternary nitrogen atom which is with a negative charge and located at 4.85 +/- 0.1 A, considered to be responsible for the nicotine-like activity. In cytisine the nitrogen atom in ring C appears at 4.8-9 A from the oxygen atom of the pyridine group and is also negatively charged.