After a laser gas nitriding treatment of the Ti-7.5Al (atom %) titanium-based alloy, we used a combination of electron backscattered diffraction (EBSD) in scanning electron microscope and electron probe microanalysis (EPMA) techniques in order to efficiently characterize the different phases in the resolidified layer. Representative measurements of chemical composition and reliable determination of crystal structure were possible for each phase of the complex microstructure. The reaction zone is formed by a mixture of isostructural TiN phases with dendritic and/or coarse needles morphology, fixed into a -Ti matrix (martensite) with a thin needle aspect. The nitrogen solubility was found to remain very low in the -Ti matrix (up to 2-3 atom %), while in the TiN phase, an aluminum solubility as high as 4 atom % was measured, reducing drastically the nitrogen content into a Ti79N17Al4 chemical composition. Copyright © 2005 John Wiley & Sons, Ltd.