For methyl transfer from choline, its alcoholic hydroxyl group must be free. Betaine and neurine are ineffective in transmethylation and are not intermediaries of the oxidative breakdown of choline. Trimethylamine oxide is as effective aerobically or anaerobically as choline aerobically; it represents the end-product of the oxidative attack on choline, and thus stands in the same relation to choline as methionine sulfoxide to methionine. Cyanide inhibits transmethylations from choline and methionine equally. It was shown, however, that the transfer enzyme for choline is a cyanide-insensitive desmoenzyme, whereas that transferring from methionine is a cyanide-sensitive lyoenzyme. There are 2 ways in which choline is broken down, viz. by choline oxidase via betaine aldehyde to betaine, and the other to trimethyl-amino oxide by a different path.