The contents of sodium, lithium, calcium and magnesium in aluminium in contact with NaF-AlF3-based melts in laboratory and in industrial aluminium cells were investigated in the temperature range 950-1030 degrees C. The experimental data were compared with a thermodynamic model. It was found that the addition of alumina or CaF2 to the NaF-AlF3 melts has only a minor effect on the equilibrium content of sodium in aluminium. Cathodic polarization enhances the content of sodium in aluminium. However, polarization has a smaller effect on the concentrations of lithium, calcium and magnesium in aluminium in industrial cells.