Phenolic compounds are frequently found in several industrial effluents. Recently, the use of hairy root cultures has been explored as a new alternative for their treatment. In this study, rapeseed and tomato hairy roots (HR) were used to remove phenol efficiently (100 to 250 mg/L) from aqueous solutions in a short time. The removal efficiencies were 95-80% and 60-70% for rapeseed and tomato HR respectively. Polyethyleneglycol (PEG-3350) addition to the reaction medium, significantly enhanced removal efficiency of rapeseed HR reaching values of 98-88%. After the removal process the acute toxicity of post-removal solutions was determined by means of AMPHITOX bioassay. Phenol solutions treated with rapeseed HR showed a lower level of toxicity than at the beginning of the treatment. Moreover, PEG addition reduced the toxicity of these solutions. On the contrary, tomato HR could only be applied to reduce the level of toxicity in solutions initially containing low phenol concentrations (100-150 mg/L), without adding PEG. From these results, it is relevant to point out the importance of studying different plant systems and their reaction capacity to find the more suitable ones for removal purposes. (C) 2010 Elsevier B.V. All rights reserved.