Abstract: A device for mixing at least two chemically reactive plastic components, includes a cylindrical mixing chamber into which plastic components are injected, wherein a reversible piston is disposed inside the mixing chamber, and a cylindrical stabilizing chamber adjoining the mixing chamber and positioned at an angle of preferably 90.degree., with a reversible cleaning piston disposed inside the stabilizing chamber for removing the reactive plastic mixture from the stabilizing chamber. In order to reduce the forces exerted on the cleaning piston by the plastic mixture and to reduce the tear-off forces on a stuck piston to a minimum, it is proposed to form on the cylindrical surface area of the cleaning piston indentations which are filled with spacer material and arranged in a manner that the cleaning piston executes a rotational motion when it moves axially.