Furnace slag from direct-to-blister smelting of Cu concns. (12.7% Cu and 3.05% Pb) was leached with NaOH soln. to remove Pb. The leaching at optimum parameters (temp. 80 degrees C, NaOH concn. 4 M, 120 min, liq/solid phase ratio 50:1) resulted in decreasing the Pb content down to 1.52% at a const. Cu content.