There are disclosed a method and an arrangement for preventing the agglomeration of crusts in a lance opening passing a wall of a metallurgical vessel and provided for a lance carrying a measuring and/or sampling probe. During the metallurgical process proceeding within the metallurgical vessel and during the taking of a measurement and/or sample by means of a lance introduced into the metallurgical vessel through the lance opening, a gas that is inert relative to a melt bath contained in the metallurgical vessel, or air, is injected into the lance opening from outside, which gas produces a gas veil at the mouth of the lance opening facing the melt bath.