The invention relates to a process for the aluminothermic welding of rails, the aluminothermically produced steel being poured into a refractory mold surrounding the rail ends which are to be joined, and alloying additives being contacted with that part of the steel which runs out of the reaction crucible and forms the weld in the rail head region, wherein the alloying with the alloying additives is carried out after the completion of the aluminothermic reaction and separation of the steel from the slag during tapping and before the steel runs into the casting cavity formed by the mold, and the overflow in the casting mold is closed.