Compositions which form homogeneous blends with lubricating oils and the like are produced by preparing a mixture of an oil-soluble dispersant (preferably a substantially neutral or acidic carboxylic dispersant) and a dimercaptothiadiazole, preferably 2,5-dimercapto-1,3,4-thiadiazole, usually with a diluent, especially a lubricant base liquid, and heating said mixture above about 100.degree. C. The compositions often contain dimercaptothiadiazole moieties in amounts substantially greater than stoichiometric. They are useful for suppression of copper activity and "lead paint" deposition in lubricants.