<jats:p>Propionylcholine, a novel analogue of acetylcholine, was identified in green plants by gas chromatography/mass spectrometry. Propionylcholine was found in the leaves of the following species previously shown to contain acetylcholine and cholinesterase activity: <jats:italic>Codiaeum variegatum</jats:italic> Blume, <jats:italic>Phaseolus aureus</jats:italic> Roxb. cv. Berken, <jats:italic>Plantago rugelli</jats:italic> Decne., <jats:italic>Populus grandidentata</jats:italic> Michx., and <jats:italic>Betula pendula</jats:italic> Roth. The quantities of propionylcholine ranged from a high of 2.3 nmol (g fresh weight)<jats:sup>−1</jats:sup> in <jats:italic>C. variegatum</jats:italic> to a low of 0.11 nmol (g fresh weight)<jats:sup>−1</jats:sup> in <jats:italic>P. rugelli</jats:italic>. These amounts represented 6 to 8% of the levels of acetylcholine. In contrast to animal tissues which rarely synthesize propionylcholine, this compound was found in all species examined which represented five families of flowering plants.