A convenient method for the rapid and high-yield synthesis of carrier-free 18F-labelled alkyl fluorides was developed. The method involves (1) preparation of carrier-free 18F-labelled silver fluoride on surface-oxidized silver wool as a fluorinating source for 18F-labelling; and (2) synthesis of carrier-free 18F-labelled alkyl fluoride by connecting the above source to a radio-gas chromatograph, followed by ordinary gas chromotographic procedure. In the present method, the carrier-free 18F-labelled alkyl fluorides are synthesized by means of nucleophilic substitution reaction in the heterogenous gas-phase system. In order to examine the usefulness of the present method, syntheses of 12 carrier-free 18F-labelled alkyl fluorides were tested using the corresponding bromo- and iodo-compounds as the reactants. Synthesis and isolation of the labelled product in each case were sufficiently rapid and efficient to allow production of usable amounts of the desired compound.