In this study the removal of arsenic by the Water Hyacinth (Eichhornia crassipes) and Lesser Duckweed (Lemna minor) was monitored under a concentration of 0.15 mg L(-1) of the element. Plant densities were 1 kg/m(2) for Lesser Duckweed and 4 kg/m(2) for Water Hyacinth on a wet basis. The arsenic was determined in foliar tissue and water samples by hydride generation atomic absorption spectroscopy. The element was monitored as a function of time during 21 days. No significant differences were found in the bioaccumulation capability of both species. The removal rate for L. minor was 140 mg As/ha d with a removal recovery of 5%. The Water Hyacinth had a removal rate of 600 mg As/ha d and a removal recovery of 18%, under the conditions of the assay. The removal efficiency of Water Hyacinth was higher due to the biomass production and the more favorable climatic conditions. This specie represents a reliable alternative for arsenic bioremediation in waters. (c) 2008 Elsevier Ltd. All rights reserved.