High-pressure density and viscosity data of polystyrene solutions in methylcyclohexane have been generated at 340, 360, 380 and 400 K using a falling-cylinder type viscometer up to 35 MPa, Measurements were conducted with two different molecular weight polystyrene samples (M-w = 50 000 and 700 000) in the concentration ranges of 3-14 wt.% (for M-w = 50 000) and 1-5 wt.% (for M-w = 700 000). Isothermal density and viscosity of these solutions increased linearly with pressure in all the concentration ranges investigated. The flow activation volume and flow activation energy of the polymer solutions were in the range of 29-55 cm(3) mol(-1) and 7-10 kJ mol(-1), respectively. It was found that the activation volume increased with temperature, and the activation energy decreased with pressure. Viscosity was correlated with density employing a Doolittle type equation eta = A exp[B/(1- V-o rho)]. The estimated closed packed volumes (V-o) from these correlations were in the range of 0.66-0.72 cm(3) g(-1) for these solutions.