Natural rubber (NR) isolated from Hevea Brasiliensis was investigated by differential scanning calorimetry, dielectric spectroscopy, and high-pressure dielectric spectroscopy. In the range of frequencies (5 x 10(-2) to 3 x 10(6) Hz). temperatures (-120 to 120 degrees C), and pressures (0.1 to 240 MPa) studied, the dielectric spectra exhibit two overlapped alpha-processes but no subglass relaxations. Thermal measurements revealed the presence of some moisture in NR. To elucidate the influence of water, dielectric measurements were carried out in dry and wet NR samples. The origin of the two dielectrically active processes was discussed in terms of (i) the apparent activation volume, (ii) the pressure coefficient of the respective glass temperatures, and (in) the values of the ratio of activation energies, at constant volume and pressure. The latter allowed extracting the relative contribution of thermal energy and volume for each dynamic process. On the basis of these results, the faster alpha-processes is assigned to the rigidified rubber backbone dynamics whereas the slower to fatty acids (such as stearic acid) that are linked to the rubber chain.