Shrub willows have demonstrated potential in many types of phytoremediation applications. Hydroponic culture was used to assess arsenic (As) tolerance and uptake by four shrub willow clones and to determine the effects of phosphate on As accumulation. After 4 weeks of growth in the absence of As, plants received one of four treatments: 0.25X Hoagland's minus P (-P), 0.25X Hoagland's minus P plus 100 microM arsenate (As100(-P)), 0.25X Hoagland's minus P plus 250 microM arsenate (As250(-P)), and 0.25X Hoagland's plus 250 IM arsenate (As250(+P)). Except for treatment As250(+P), phosphate was excluded due to its tendency to interfere with As uptake. After 3 weeks of treatment, plants were separated into root, leaf, and stem tissues. Biomass production and transpiration were used to quantify As tolerance. There was wide variation among clones in As tolerance and uptake. The presence of phosphate in solution alleviated the negative impacts of As on biomass and transpiration and also increased above ground As accumulation, suggesting that phosphate may play a role in reducing toxicity and enhancing As uptake by willow shrubs. These findings offer insight into As tolerance and uptake in Salix spp. and add to the growing body of evidence supporting the use of shrub willow for phytoremediation.