Rates of adsorption and desorption, of di-isopropyldithiophosphoric acid and tetraisopropylthioperoxydiphosphate from hexade-cane on to steel, have been measured wing14C radiolabelled compounds. Concentration, temperature, and stirring dependence have been examined. The adsorption is surface controlled and the kinetics can be represented by a Langmuir model. Correlation of rate data with antiwear properties is examined.Presented as an American Society of Lubrication Engineers paper at the ASLE/ASME Lubrication Conference in Hartford, Connecticut, October 18–20, 1983