Abstract: The present invention describes an agent for the desulfurization of pig iron or cast iron, based on finely granulated magnesium and at least 3 w. % of an metallurgically silicious mineral with a bond, blend or crystal structure and/or one of the minerals syenite and/or rhyolite pure or as a mixture.The desulfurizing agent may contain as an additional compound calciumcarbide and/or calciumoxide. The magnesium granule may be coated with these components.This agent is preferrably fed to the iron melt either as a mixture or in the co-injection process as one compound through a lance where mixing is achieved with the second compound before entering into the iron melt.