In the present paper are discussed some thermodynamic aspects related with the analysis of the fine structure of the thermally stimulated depolarization currents spectrum. The physical significance of the so-called compensation law is analysed and it is suggested that the lag between the compensation temperature and the glass transition temperature is related to the breadth of the glass transition. It is also shown that the plot of Delta s(not equal) vs Delta H-not equal for the different elementary components of the global spectrum shows ’groupings’ of relaxations which allow one to distinguish the different relaxation processes.