Abstract: When metal inert gas (MIG) welding is carried out at normal atmospheric pressure, the electrode is made positive with respect to the workpiece because the use of a negative electrode gives little penetration. In undersea welding, as the pressure increases the arc stability and metal transfer in MIG welding become erratic and there is copious fume evolution. According to the present invention, MIG welding at pressures greater than 7 bars is carried out with the electrode negative with respect to the workpiece and with an electrode wire of diameter not greater than 1.4 mm; the slope of the power supply, as seen from the welding arc, is preferably between 6 and 15 V/100 A, which is higher than the 3 to 4 V/100 A used in positive-electrode MIG welding at normal atmospheric pressure.