The paper describes a new apparatus to measure tensile creep curves of polymer/volatile organic compound (VOC) systems, especially designed for measurements of small VOC loadings in glassy polymers. For the first time creep curves for glassy polymer/VOC systems are recorded. The measurements were performed for the system polystyrene/toluene at different toluene loads up to w(toluene) = 0.13 and at temperatures of 30, 50, and 70 degrees C. It was found that increasing VOC mass fractions qualitatively influence the mechanical properties of a polymer in the same way like increasing temperature does. Since at isothermal conditions these properties are affected by the glass transition of the system, this information for the polystyrene/toluene mixtures was used to modify and to verify the correlation of Kelly and Bueche to predict the glass-transition temperature of polymer/solvent systems.