A novel temperature-step experimental method that extends the Bodiguel-Fretigny liquid dewetting method of investigating polymer thin films is described and results presented from an investigation of thickness effects on the glass transition temperature (Tg) of ultrathin polystyrene (PS) films. Unlike most other methods of thin film investigation, this procedure promises a rapid screening tool to determine the overall profile of Tg versus film thickness for ultrathin polymer films using a limited number of samples. Similar to our prior observations and other literature data, with this new method obvious Tg depression was observed for PS thin films dewetting on both glycerol and an ionic liquid. The results for PS dewetting on the two different liquids are similar indicating only modest effects of the substrate on the Tg-film thickness relationship. In both instances, the Tg depression is somewhat less than for similar PSs supported on silicon substrates reported in the literature. (c) 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2013, 51, 1343-1349