The subject of the invention is a novel process for the preparation of N-[2-n-butyl-3-{4-[(3-di-n-butylamino)-propoxy]benzoyl}benzofuran-5-yl]-methanesulfonamide of formula I: and pharmaceutically acceptable salts thereof wherein the acyl group of the benzofuran derivative of the general formula II: where R represents C1-4 alkyl-, C1-4 alkoxy- or aryl group, is selectively cleaved and if desired, the resulting compound of formula I is transformed into its salt.