The use of deep-rooted woody plants offers a means of remediating and stabilizing Arsenic (As)-rich contaminated soil and tailings often associated with mining activities. However, precisely how these plants respond to arsenic is not well understood. Studies on the responses of eucalypts to high levels of arsenic show variation in both performance and As-uptake. For example, in studies on sugar gum (Eucalyptus cladocalyx) relative growth rate was reduced by 50% and accumulated 99% of As in the roots, ranging from 111 to 746 %mu;g/g d.w. Tissue As was found to be in a reduced form, As III, coordinated to PhytoChelatins (PCs), largely as AsIII-PC 3. Oxidized PC 2 was also present ranging from 143 to 347 %mu;g/g f.w. Cellular localization studies further showed As-complexation to occur in the root endodermis with undetectable amounts in the vascular bundles. These results suggest that arsenic complexes play an important role in As-tolerance, and that selective breeding of eucalypts with enhanced-PC synthesis may help in the improvement of As-mine-site stabilization.