The relation between the temperature Tαof the dipolar relaxation, obtained by the technique of thermally stimulated currents (TSC) and the glass transition temperature Tghas been studied in amorphous poly(ethylene terephthalate) samples. The temperature Tαdepends fundamentally on the polarization temperature Tp, the polarization time tp, and the heating rate v. For each heating rate a maximum Tα, TM, was obtained for an optimum polarization temperature Tpo. The value of Tpois 70°C, independent of the heating rate, and very close to the glass transition temperature obtained by differential scanning calorimetry (69°C). The resulting value for TMcoincides with Tpoin the limits of null heating rate and null isothermal polarization time, and, consequently, TMgives the value of the glass transition temperature for each heating rate as a function of the isothermal dipolar contribution on polarizing at the temperature Tpo.