Abstract N-(2-[18 F] fluoroethyl)-N′-methylthiourea ([18 F] FEMTU), a fluorine-18 labelled derivative of the hydrogen peroxide scavenger dimethlthiourea (DMTU), has been synthesized by reaction of 2-[18 F] fluoroethylamine with methylisothiocyanate. 2-[18 F] Fluoroethylamine was obtained in modest radiochemical yields (39±6%, mean±sd, n= 5, decay corrected) by nucleophilic substitution with [18 F] fluoride on N-[2-(p- ...