The invention relates to the use of polyorganosiloxanes having 3 or more siloxane units, which has (i) at least one organic component R1, where R1 has at least one carbon-carbon multiple bond, and (ii) at least one hydrocarbon component R2, where R2 has a chain length of 5 to 50 carbon atoms. The polyorganosiloxanes are used in the processing and vulcanization of rubber and are incorporated reactively into it. They give rise to a lowering in the viscosity of the rubber in the course of processing and in some cases to an improvement in the mechanical properties of the vulcanized rubber.