Abate (O,O,O',O'-tetramethyl-O,O'-thiodi-p-phenylene phosphorothioate) is a larvicide suggested for the control of mosquito larvae in natural waters. Data are needed for Abate residues in water in order to determine the levels which will result from the routine use of this compound in drinking waters. The injection of a large number of Abate samples in the gas chromatograph contaminate the instrument with the result that Abate peaks appear with the solvent injection only. The following investigation is concerned with the quantitative conversion of the low vapor pressure 4,4'-thiodiphenol to a product of high vapor pressure using silylating reagents.