Two sites with five wells in the Danube-Tisza interfluvial were studied in order to help understand the genesis of the high-As content of shallow ground water. Separation of As species was carried out in the field as it proved to be the best method by which to preserve the As species. Different geochemical environments could be separated by the speciation studies which correlate with the concentrations of oxyanion-forming elementss uch asV, Se, Mo, U and W.