Dimethylaminomethyl acetate, a postulated intermediate in the Polonovski reaction, has been isolated for the first time in 80% yield from the reaction between trimethylamineN-oxide and one equivalent of acetic anhydride. With more acetic anhydride the dimethylaminomethyl ester gaveN,N-dimethyl acetamide and two other products which have been identified as 2-(dimethylaminornethyl)acrylic acid and 2,2-bis(acetoxymethyl)-3-(dimethylamino)propionic acid. The manner of formation of these two products has been clarified by using deuterium and13C labelled reagents.Hydrolysis of deuterated dimethylaminomethyl acetate prepared from trimethyl-d9amineN-oxide and acetic anhydride gave satisfactory yields of dimethyl-d6amine and formaldehyde-d2.