The production and use of [ 18F]fluoromethyl triflate ([ 18F]CH 2FOTf), a more reactive [ 18F]fluoromethylating agent than [ 18F]fluoromethyl bromide ([ 18F]CH 2BrF), is described. [ 18F]CH 2FOTf was prepared from [ 18F]CH 2BrF. The latter was synthesized by nucleophilic substitution of CH 2Br 2 with no-carrier-added [ 18F]fluoride and purified by four Sep-Pak Plus silica cartridges connected in series. It was then quantitatively converted on-line to [ 18F]CH 2FOTf by passing through a heated AgOTf column. Decay-corrected radiochemical yields of [ 18F]CH 2FOTf based on [ 18F]fluoride were 47±8% ( n=20). Both [ 18F]CH 2BrF and [ 18F]CH 2FOTf were applied to solid-supported [ 18F]fluoromethylation of N,N-dimethylaminoethanol on a Sep-Pak Plus C18 cartridge to produce the 18F-labeled choline analogue, ( β-hydroxyethyl)dimethyl-[ 18F]fluoromethylammonium ([ 18F]fluorocholine). Depending on flow rate and amount of precursor used, decay corrected radiochemical yields of [ 18F]fluorocholine from [ 18F]CH 2BrF ranged from 6% to 63%, while [ 18F]CH 2FOTf afforded yields of more than 80%. Thus, by using the latter reagent and a subsequent purification on a Sep-Pak Accell CM cartridge, [ 18F]fluorocholine was produced from [ 18F]fluoride in overall radiochemical yields of 40% (decay corrected) in less than 30 min.