A process and a mixing head for the production of a reaction mixture comprising at least two reaction components, with a high degree of mixing. By this process, reaction components are introduced, at a high pressure into one end of the mixing chamber of the mixing head, these components being deflected by the front of the discharge piston which forms the opposite end of the chamber, a counterflow forming intensive turbulences on the wall of the mixing chamber and on the boundary surface with the incoming flow before this counterflow exits the mixing chamber at the same end through which it entered the chamber, substantially as a radially-directed, laminar flow.