The effect of some processing aids, Redex-2, Redex-SP-2, and Redex-A, on rheological properties, tensile properties, and dynamic mechanical properties of natural rubber compounds has been studied. The optimum level of these additives was determined and the changes caused by the use of these additives were evaluated by comparison with an additive-free control compound mixed under similar conditions. Redex-2 and Redex-SP-2 improve the processability of the natural rubber compounds, giving a reduction of both Mooney viscosity and shear viscosity, but the concentration of the processing aid necessary to this improvement is different; the optimum concentration is 1.75 phr on Redex-2 compounds, and the optimum concentration is 3 phr on Redex-SP-2 compounds. However, Redex-A behaves as a plasticizer, reducing the Mooney viscosity, the shear viscosity, and the Tg, improving behavior at low temperatures. The optimum proportion is 3 phr. The behavior of these processing aids is related to the temperature, too. (C) 2004 Wiley Periodicals, Inc.