The Soret coefficient S T and collective ͑mass͒ diffusion coefficient D c of polystyrene dissolved in the good-solvent toluene has been measured over a range of concentrations and molecular masses with an optical beam-deflection method. Our measurements indicate that S T scales inversely with the polymer translational diffusion coefficient in dilute solutions, exhibits a power-law scaling with polymer concentration, and an independence of polymer molecular mass in semidilute solutions. These findings are consistent with the known scaling of 1/D c in dilute and semidilute polymer solutions, the relative insensitivity of the thermal-diffusion coefficient D th of polystyrene in toluene to polymer concentration, and the relation S T ϭD th /D c from irreversible thermodynamics. We are able to represent our S T and D c data by theoretically motivated reduced-concentration master curves, but the concentration-molecular mass scaling variables are found to be different for each transport property, a result contrary to theoretical expectations. However, the asymptotic concentration scaling exponents deduced from these data fits are compatible with de Gennes' scaling arguments for D c and with modern estimates of the chain-size exponent for swollen polymers in good solvents.