Ocimum basilicum L., Basil, has shown to be a bioremediator candidate for the organochlorinc pesticide endosulfan. Nevertheless, the mechanism of phytoremediation of the pesticide is still unknown. Glutathione-S-Transferase (GST) is an enzyme involved in plant defense against pollutants and Olddative damage. Because of this, GST activity changes would be expected after an exposition to endosulfan. Thus, to evaluate the response of basil to endosulfan exposure, we measured GST activity in leaves, roots, stems and rhizosphere. Plants were exposed lo O, 10, 100, 1000 mg endosuIfan/Kg of soil. The GST activity increased after endosulfan exposure depends on organ and endosulfan concentration. In leaves, GST activity increased at 10 mg/Kg, but decreased at 1000 mg/Kg. Root GST activity was increased al 10 mg/Kg, but became normal at higher concentrations of endosulfan. GST activity from stem and rhizosphere showed no significant variation with the endosulfan concentration.