Abstract: A modular abrasive agent water jet cutting head (1) has a nozzle (4) issuing a high-speed water jet (16), a mixing chamber (10) through which the high speed water jet passes (16), an abrasive agent supply line (14), and a focussing nozzle (15) forming the outlet of the mixing chamber (10). A dosing unit (12) has an axial passage of the high-speed water jet (16). The passage (18) has one or more expansions or channels (11) extending radially and which are of reduced cross section at the passage. There are preferably in each case are formed as a slits, which are only slightly wider than the diameter of the thickest abrasive particle. The expansion or channel (11) is closely connected to the passage of the high-speed water jet (16) and introduces the abrasive agent into a chordal section of the water jet (16) which is oriented in the direction of the cutting action. From there the high-speed water jet (16) receives a track of abrasive agent on its surface.