A comparative study of the different relaxations present in poly(ethylene-2,6-naphthalene dicarboxylate) (PEN) is carried out by thermally stimulated depolarization current (t.sc.), dynamic mechanical analysis (d.m.a.) and dynamic electric analysis (d.e.a.). In the temperature range from - 150 to 200 degrees C, PEN shows four relaxations located, in increasing temperature order, around - 70 degrees C (beta), 60 degrees C (beta*), 130 degrees C (alpha) and 170 degrees C (rho). The two sub-glass transition relaxations detected are attributed to dipolar motions of the polymer chain and their origin is discussed. Above the glass transition (a relaxation) the rho peak is shown to be of non-dipolar origin and associated with free charge detrapping in the material. The kinetic parameters of the relaxations observed by these techniques in the aforementioned temperature range have been determined by fitting the experimental data to standard models. The activation energies calculated in this way vary from 0.5 eV for the beta relaxation to 2.2 eV for the rho relaxation. The beta* and a relaxations are distributed and it is shown that they follow the compensation law.