The paper treats the effect of hydrogen in argon as a shielding gas in are welding of austenitic stainless steel. The studies were carried out in TIG (Tungsten Inert Gas) welding with a non-consumable electrode and MIG (Metal Inert Gas) welding with a consumable electrode, in both cases with different volume additions of hydrogen to the argon shielding gas, i.e., 0.5, 1.0, 5.0, 10 and 20%. The studies showed that hydrogen addition to argon changes the static characteristic of the welding arc. The hydrogen addition to argon increases are power and, consequently, the quantity of the material melted. In TIG welding a 10% addition of hydrogen to argon increases the quantity of the parent metal melted by four times. The hydrogen addition increase thermal and melting efficiencies of the welding arc too. The process stability in TIG welding in the mixture of hydrogen and argon is very good. Also in MIG welding, the hydrogen addition to argon increases melting rate and melting efficiency of the are, but the increase is much smaller than in TIG welding. Since hydrogen is a reducing gas, the weld surface produced by hydrogen addition to argon is in both cases very clean and without oxides. (C) 2000 International Association for Hydrogen Energy.