The title reduction of nitroaromatics ArNO(2) by vinyl halide radical cations CH(2)[double bond]CH-X(+*)(X = Cl or Br) to form arylnitrenium ions ArNH(+) involves a change in oxidation number of nitrogen from +3 to -1. This novel reaction provides a new route for the generation of arylnitrenium ions, a highly selective method for the detection of explosives in mixtures, and offers clues to the carcinogenic activity of nitroaromatics in vivo.