A universally accepted criterion when assessing blend compatibility is the existence of a single glass transition temperature, which changes as a function of blend composition. Differential scanning calorimetry and dynamic mechanical strain spectra are powerful tools in the study of polymer relaxation in the glass transition zone. In this research both techniques are employed to determine the glass transition temperatures of a series of polymer blends based on polyvinylidene fluoride. In the light of the data obtained further thought is given to the discrepancies between the results obtained with one and the other method, as well as to the compatibility of the experimental blends.