A simple, rapid, and sensitive procedure for the study of sulfatase kinetics using nonchromogenic substrates is described. The procedure utilizes the dye potassium rhodizonate which forms a complex with barium ions resulting in a pink color. The extent of reduction of the pink color in the presence of sulfate ions indicates the quantity of sulfate. Some of the factors other than SOd2-which can influence the pink color intensity of the rhodizonate-barium complex are described. The optimum conditions for the determination of sulfate are investigated. The assay procedure has good reproducibility and has a lower limit of detection of about 1 nmol of S0,2-when low Ba*+ concentrations are used. A comparative study of the rate of hydrolysis of a number of different substrates by aryl sulfatase A using this method as well as an independent, spectrophotometric method is described. The maximum variation between the two procedures is 5% which is within the possible uncertainty in the standard curves and the error in the molar extinctions used for the estimation of products. The method is substantially more accurate and convenient than previously described methods which required chromatographic separations, radioactive substrates, etc.