Physical ageing in polystyrene (PS) has been studied by means of modulated differential scanning calorimetry (m.d.s.c.). The results show that there exists a characteristic annealing temperature at which relaxation enthalpy has a maximum value. When annealing below 65 degrees C, another relaxation peak has been found. The position of this relaxation peak, which changes with annealing temperature, lies approximately between 54 and 64 degrees C. It has been postulated previously in the literature that the relaxation behaviour involves phenyl ring relaxation. As measured from heat capacity curves, this transition is evident as a shoulder on the glass transition. With increasing annealing temperature, the glass transition of PS increased slightly.