This paper-presents a study on the growth of oxides on a commercial chromia-forming alloy (austenitic stainless steel AISI 304), in air at 900 degreesC. After the nitridation treatment performed, a gamma(N) solid solution is observed without any nitride formation in the alloy surface. In situ X-ray diffraction has been used to follow oxides evolution at the testing temperature. At the beginning of the oxidation test, Fe2O3 is formed together with Cr2O3 and Mn1.5Cr1.5O4. Nevertheless, Fe2O3 quickly becomes undetectable and appears again after 30 h oxidation. In the case of untreated specimens, four oxides are observed throughout the oxidation test: Cr2O3, Mn1.5Cr1.5O4, Fe2O3 and Fe7SiO10. Our results show that nitridation increased the high temperature oxidation resistance of the 304 stainless steel at 900 degreesC. (C) 2003 Elsevier B.V. All rights reserved.