A recent surge of interest in sulfur in the environment has revealed the need for improved methods of analysis for sulfate, SO4=, in rain, freshwater and sediment interstitial fluids. Ion chromatography permits the rapid determination of SO4= in the ppm range (1 ppm = 1 mgL'1 = 10 μmol L-1 sulfate) on relatively small samples with good specificity. If a suitable instrument is available, this technique is a good choice for many environmental analyses. Other approaches to sulfate analysis are based on its precipitation with organic or heavy metal cations, usually barium or lead. The amount of precipitate formed may be determined by inter alia gravimetry, turbidimetry, radiometry (using 133-Ba), atomic absorption spectrophotometry (Ba or Pb detection), potentiometry (using a Pb++ ion selective electrode) , colorimetry, or by x-ray fluorescence spectrometry (Ba, Pb or S detection)(1). Because of our experience with x-ray fluorescence analyses, we chose to develop and test a procedure using that technique.