Intermetallic alloys based on titanium aluminides, especially gamma-TiAl (Ti-50at.%Al), are of great attraction for structural high temperature applications e.g. in aero engines because of their low specific weight (about 4g/cm(3)) and their good mechanical properties at elevated temperatures. However, the use of TiAl alloys is still limited to a temperature of approximately 750degreesC due to their poor oxidation resistance at higher temperatures. The oxidation behaviour of TiAl alloys has to be improved before these alloys can be used at temperatures of 800degreesC and above. The improvement of the oxidation resistance of gamma-TiAl can be achieved by small amounts of halogens F, Cl, Br and I (so called halogen effect). The halogens can be incorporated in several ways e.g. by ion implantation. In this paper results of a technical TiAl alloy called gamma-MET [Ti-46.5Al-4(Cr, Nb, Ta, B)] with and without implantation are presented.