ZINC DIHYDROCARBON-SUBSTITUTED DITHIOPHOSPHATES, AND IN PARTICULAR ZINC DIARYL DITHIOPHOSPHATES, ARE PREPARED BY NEUTRALIZING THE DIHYDROCARBON-SUBSTITUTED DITHIOPHOSPHORIC ACID WITH ZINC OXIDE IN THE PRESENCE OF A NEUTRALIZATION PROMOTER WHICH IS A ZINC SALT SUCH AS ZINC NITRATE, ZINC CHLORIDE, ZINC SULPHATE, AND THE LIKE; THE ZINC SALT MAY BE ADDED AS SUCH OR FORMED IN SITU BY THE ADDITION OF NITRIC ACID, HYDROCHLORIC ACID OR SULFURIC ACID TO THE MIXTURE OF THE DIHYDROCARBYL DITHIOPHOSPHORIC AND SUFFICIENT ZINC OXIDE TO NEUTRILIZE THE DITHIOPHOSPHORIC ACID AND TO FORM PROMOTING AMOUNTS OF THE INORGANIC ZINC SALT.