The influence of implanted chromium and yttrium on the oxidation behaviour of Ti-50Al (at %) in air at 800 degrees was investigated. It was found that implanted chromium and/or yttrium leads to a decrease of the oxidation rate because an alumina scale was formed on the implanted material in the early stages of oxidation, whereas a titania-based scale grew on the non-implanted material. With increasing oxidation time the difference in oxidation behaviour between the implanted and non-implanted alloy gradually disappeared. These results show that chromium and yttrium, provided their concentration is properly chosen, can have a similar positive effect on the oxidation behaviour of TiAl-based intermetallics as they have on the oxidation behaviour of conventional Fe-, Ni-, or Co-based alumina-forming high temperature alloys.