Polymeric dyes are environmental pollutants widely used in the textile industry. Polymeric dyes have a structure analogous to common polycyclic aromatic hydrocarbons (PAHs). Plants that possess an inherent tolerance to these dyes are currently being investigated for use in phytoremediation. Tolerant plants create a healthy rhizosphere for microbial degradation and contribute to uptake of pollutants from soil or water. Tolerant plants have been found to contain high levels of endogenous phenolic compounds, which contribute to plant stress response mechanisms. Peroxidases are a ubiquitous group of enzymes known to participate in the oxidative coupling of phenolic compounds during the lignification process. Four elite clonal lines of Mentha pulegium were screened for high phenolic content on different concentrations of polymeric dye labeled R-478, a violet colored anthraquinone dye. One of the four clonal lines, MPH-4, showed a significant correlation between phenolic content and peroxidase activity in response to the polydye R-478. MPH-4 was chosen for further screening with polydye R-478 in conjunction with Agrobacterium rhizogenes. The use of A. rhizogenes was based on the rationale that the bacterium would induce root development and enhance dye uptake. Although the expected results were not observed, the changes seen in the innoculated plants may be due to the diversion of key metabolites from the primary metabolism towards cytokinins. (C) 2002 Elsevier Science Ltd. All rights reserved.