New 21-cm observations of Messier 31 are used to measure its rotation curve up to a radius of ~40 kpc. The observations were obtained at the Effelsberg 100-m telescope and extend by ~15 kpc the radius of the last measured point of the rotation curve. A preliminary model of the mass distributionshows that at the last observed velocity point, the dark–to–luminousmass ratio is ~1 for a total mass of ~4.5 × 1011 M๏, whichvalue is comparable with that of the Milky Way. This exploratory project is ongoing and other Hi observations using other radio-telescopes are planned to confirm this result, as well as a mosaic of the Hα emissionline.