Abstract: Acetylcholine(I;X=OH,n=1)is a substance possessing intense physiological activity toward the vegetative nerves.It would be interesting to see the variation of physiological activity in the homologous series of choline esters(I). C_nH_2n+1·CO·OCH₂·CH₂·N⁺(CH₃)₃X^- (I) The literature methods for the preparation of choline esters either by the interaction of β-halogen-substituted ethyl esters with trimethylamine or by the acylation of choline salts are not satisfactory in the purification of the products. Loury prepared a few choline ester salts by the acylation of 2-dimethylaminoetha- nol and the subsequent quaternization of the tertiary amines so obtained,but he did not give the details including the physical constants and the analyses of the products.In the present work this method has been extended,a series of fatty acid esters of choline iodide has been synthesized.The products are well-defined crystalline solids.The lower members of the series are soluble in water,methanol or ethanol;the higher members are only slightly soluble,and the solid substances are greasy and the solutions are soap-like.The higher members gave two melting points,heating to high temperature caused the decomposition of these compounds, trimethylamine hydroiodide was isolated in several cases. When these compounds were used on the isolated rabbits' heart the lower members produced an acetylcholine-like effect,i.e.a slowing of the heart rate, the octanoyl compound was more or less inactive,and from then onwards with increasing chain-length an increasing degree of inhibition of the response to acetyl- choline was produced.From the decanoyl compound onwards with increasing chain length they inhibited spontaneous gastric secretion and the secretion of the vagotomised stomach stimulated by prostigmine in the rats as well if administered intramuscularly.