We analyzed the steady state behavior of a thermogravitational column for a toluene-polystyrene system at different concentrations and at molecular weights of polystyrene in the 45 000-540 000 range. The results obtained indicate that steady state separation strongly increases with concentration and molecular I weight. From steady state separation measurements, the thermal diffusion coefficient of the mixtures considered was determined. It is shown that this quantity is in the dilute region, irrespective of molecular weight and concentration. The close agreement between our values and those reported in the literature obtained using different techniques indicates that closed columns can be used to accurately determine thermal diffusion properties of macromolecular solutions.