This contribution gives the first results of an ongoing research aiming at developing a new surface treatment technique using a supercritical nitrogen jet, named Jazolthop, for surface modification. As nitrogen is naturally recycled within air, this new process has a high potential for surface treatment without any chemical, physical or sewage effluents. This contribution shows that, pending on the operating condition, the technique can be used (i) under a stripping or ablation mode as well as, in a ``less conventional'' approach, (ii) for surface hardening. Illustration of the ablation mode is given for a Ti-6Al-4V alloy treated under static conditions using an intrusive jet. After 2 min of treatment, a thickness of 200 mu m was removed from the surface by successive stripping out of micro-chips. Illustration of the hardening mode is given through the analysis of stainless steels treated under the cryogenic jet at a moving torch velocity of 5 mm/min. The jet conditions were selected to be less intrusive and trigger the martensitic transformation without creating surface flaws of micro-cavities. In this case, the hardness of the steels was more than doubled after the passage of the cryogenic jet.