The scaling law for relaxation times (tau's) recently proposed by Casalini and Roland was used in the framework of Kovacs, Aklonis, Hutchinson, and Ramos phenomenological theory. With this approach, it was shown that both the isobaric and the isothermal glass transitions of polystyrene can be reliably predicted with only two fitting parameters, namely, tau in the reference state and the fractional exponent that describes the dispersion of the alpha relaxation. (C) 2011 Wiley Periodicals, Inc. J Appl Polym Sci 122: 3752-3757, 2011