Softening of cold-drawn wires of a tough pitch copper containing a small amount of lead as well as oxygen and sulphur is enhanced when hot-rolled rods of the copper are heated at 600 degrees C before cold-drawing. Enhancement causes were examined using wires of pure Cu, Cu-O, Cu-S, Cu-Pb, Cu-Pb-O, Cu-Pb-S, Cu-Pb-S-O. The softening enhancement appearing in the Cu-Pb-S-O specimen was attributed to the decrease in the amount of dissolved Pb and S in the copper matrix due to precipitation during heating at 600 degrees C. The addition of lead in the presence of oxygen was shown to decrease the solid solubilities of S in the copper matrix.