The polyfluoroarenes m-H2C6F4, m-02NC6F4H, m- and p-BrC6F4H, Cp-HC6F4)2, C6F5H, 1, 3, 5- F3C6H3 and m-FS02C6F4H have been thallated by thallic trifluoroacetate in fluorosulfuric acid in the presence of antimony pentafluoride. Substantial dithallation of m-H2C6F4 and 1, 3, 5-F3C6H3 and slight trithallation of the latter have been achieved. The products were identified by conversion into the corresponding polyfluoroiodoarenes on reaction with aqueous sodium iodide. From the reaction with pentafluorobenzene, pentafluorophenylthallium(III) species have been characterized. l, 2, 4, 5-Tetrafluoro-3-methoxybenzene was thallated by thallic trifluoroacetate in 1, 2-dichloroethane in the presence of boron trifluoride etherate, but C6F5H and p-MeC6F4H failed to react.