Abstract: A continuous process for the fuming treatment of metallurgical slag, e.g. lead and copper smelting furnace slag. Passing the slag continuously through consecutive slag treatment zones of a fuming furnace, subjecting it in a first one of said zones to heating to fume off comparatively volatile, preferably sulphide-bound constituents thereof, subjecting it in a second one of said zones to reduction to reduce preferably oxide-bound constituents and fuming off said last mentioned constituents in an elementary form and adjusting the temperature of the slag in said first zone such that the reduction treatment in said second zone is accomplishable substantially without further heating the slag.