An investigation was carried out seeking to correlate the results of enthalpic and viscoelastic measurements of the progress of structural relaxation in glassy polymers. Experimentally, changes in enthalpy were followed by calorimetry, and changes in the viscoelastic response by stress relaxation. The Narayanaswamy/Moynihan model was used in the simulation of enthalpy relaxation. An optimized set of model parameters was determined, for which the calculated enthalpy relaxation times were comparable to the experimental stress relaxation times, thus providing an empirical link between two different manifestations of the same process.