A method has been developed for the determination of total sulfur in fluoride salts using the methylene blue procedure. Reduction of sulfate to hydrogen sulfide is achieved through the use of a new reducing mixture consisting of stannous chloride dissolved in concentrated phosphoric acid. The new mixture is effective on microgram amounts of sulfate and offers a major advantage over the red phosphorous reducing mixtures in that larger samples may be taken for analysis. The procedure has been applied to fluoride salts containing from 1 to 500 ppm of sulfur. The coefficient of variation the method is 10 percent.