This disclosure relates to a process for the preparation of N-[2-n-butyl-3-{4-[(3-dibutylamino)-propoxy]-benzoyl}-1-benzofuran-5-yl]-methane-sulfonamide of formula I and its pharmaceutically acceptable salts, wherein one of the methylsulfonyl groups of the 2-n-butyl-3-[(di-n-butylamino-3-propoxy)-benzoyl]-5-bis-(methylsulfonamido)-benzofuran of formula II is selectively cleaved and if desired, the resulting compound of formula I is transformed into its salt.