Several cationic dyes were evaluated as reagents for the spectrophotometrlc determination of anionic surfactants. Of the dyes examined, ethyl violet was the most useful reagent. By use of this dye, trace amounts of anionic surfactants could be extracted Into benzene and toluene In a single extraction and determined spectrophotometrlcally at 615 nm; the molar absorptivity was about 1 X 10s L mol-1 cm-1 and the absorbance of the reagent blank was 0.01. The method could be applied to the determination of parts-per-bllllon amounts of anionic surfactants In waters with satisfactory results.