The thermodynamics and kinetics of the sulphurization and desulphurization of D. R. I. wustite, and magnetite were studied. The equilibrium constants of the reactions were determined from calculations based on published thermodynamic tables, and a thermogravimetric technique was used in the study of the kinetics. Sulphurization was effected by the use of either hydrogen sulphide or carbon oxysulphide. The possibility that wustite or magnetite may react with sulphur in the preheating zone of the kiln, which was indicated by the thermodynamic study, was confirmed by the kinetic study. Heating of the kiln charge at a high rate under oxidizing conditions is suggested for the improved transfer of sulphur from the ferrous charge to the gaseous phase.