Prebiotic synthesis of choline. Prebiotic syntheses of amino alcohol-containing phospholipid headgroups would have been contingent on the availability of free amino alcohols. On early Earth, ethanolamine (EA) and N-methylethanolamine (MEA) could have been formed on reaction of glycolaldehyde with ammonia. Ensuing reductive methylation of EA with formaldehyde could have produced MEA and N,N-dimethylethanolamine (DEA). However, no prebiotic synthesis of choline (Ch) has been reported to date. A biosynthetic route leading to Ch entails sequential N-methylation of EA. In each step, the methyl group is provided by S-adenosyl methionine, and the reactions are catalyzed by Nmethyl transferases. Recently, the reaction of methylamine with nitroprusside in alkaline solution was shown to afford a transient, prebiotically plausible methylating agent. We thus wondered whether Ch could be produced by methylation of DEA using the methylamine-nitroprusside system.