The reactivity of multi-walled carbon nanotubes with some inorganic fluorides (BF3, TiF4, NbF5 and WF6) has been studied. The accommodation of the fluorinated species into the carbon lattice has been shown to result from intercalation and adsorption/condensation phenomena. Charge transfer, induced by such a chemical doping, has been clearly evidenced by F-19 NMR and ESR spectroscopy. The doped materials exhibit insulating properties. Due to a restriction in size of the intercalated domains, the opportunity of achievement of a homogeneous doping level and of resulting isotropic 1D transport properties in chemically modified carbon nanotubes is discussed. (C) 2003 Elsevier B.V. All rights reserved.