Mentha pulegium elite clonal line MPH-4 is known to contain high levels of endogenous phenolic compounds. These compounds are secondary metabolites of the phenylpropanoid pathway that aid in several metabolic processes, including stress response and hormone production. Agrobacterium rhizogenes is a soil bacterium utilized for its ability to transfer its Rol genes via the Ri plasmid on t-DNA. A. rhizogenes is also known to increase secondary metabolites in several plant varieties. In this study, MPH-4 and A. rhizogenes were used to demonstrate how secondary metabolite production can be effected. Total plant phenolics and GPX activity were enhanced by inoculation of tissue culture explants with A. rhizogenes. Enhancement of phenolic production by A. rhizogenes was more apparent when explants were also treated with polymeric dye R-478. The response of MPH-4 to A. rhizogenes and polydye R-478 are useful to determine the use of this clonal line in phytoremediation. (C) 2002 Elsevier Science Ltd. All rights reserved.