a b s t r a c t The combined local dynamics and free volume investigations in a series of fourteen glass-formers by means of electron spin resonance (ESR) and positron annihilation lifetime spectroscopy (PALS) are pre-sented. The reorientation of the spin probe TEMPO is related to the annihilation of the ortho-positronium (o-Ps). It was found that the slow to fast transition at T 50G is characterized by the almost constant o-Ps lifetime, s 3 (T 50G) = 2.17 ± 0.15 ns. Then, this transition is connected with the occurrence of the mean free volume hole fluctuation of V h (T 50G) = 114 ± 15 Å 3 nearly independent of the chemical and topological character of the matrix constituents as well as of the type and extent of intermolecular interactions.