Abstract: The invention relates to a method and a device for the physicochemical treatment of fluid media. The aim of the method is to modify the surface tension and the viscosity of the fluid, to mechanically reduce and eliminate organic and/or inorganic substances, micro-organisms, such as for example microbes, bacteria, fungi or algae and to chemically oxidise or reduce substances and material compounds entrained by the fluids. According to said method, energy is supplied to the fluid that is to be treated as follows: at least two volumetric flows of the fluid are guided at high speed, so that their surfaces intermingle or collide with one another in the form of a translational and/or rotational motion at a different speed, if the flows originate from the same direction, or at a selectable speed, or optionally an identical speed, if the flows originate from opposite directions.