In general, the crystallographic preferred orientation of grains in thin films changes during the deposition process. Reflection high-energy diffraction (RHEED) is a surface sensitive method allowing a qualitative as well as a quantitative texture analysis during film growth. To show the strength of this new method in texture research, results are presented of a real time in-situ RHEED investigation on MgO thin film growth using pulsed laser deposition in combination with ion-beam assistance. Without an ion beam strong fibre textures are observed depending on temperature as well as on film thickness. Using ion incidence angles between 35degrees and 55degrees in the nucleation stage a strong cube texture develops above 250degreesC on amorphous substrates. The in-plane alignment determined by RHEED analysis is better than 21degrees. Above a film thickness of 5 to 10 nm the texture changes in such a way that the <100> direction becomes parallel to the ion beam. This change can be explained by anisotropic sputter rates and stress induced effects found in experiments on MgO single crystals.