The relation between Cd and oxidative stress in BY2 cell cultures of tobacco was studied. In response to 5 mM Cd, a rapid generation of H2O2 has been detected in tobacco cell cultures by the oxidative quenching of the fluorescent reporter dye pyranine. This oxidative burst reached the maximum production of H2O2 after 10 min of treatment with Cd. This response could be considered as short term hypersensitive response previous to the oxidative stress caused by the metal at the cell plasma membrane. The observed antioxidant enzymatic response to the oxidative burst was preceded by an increased peroxidation of lipids with a significant increase in the activities of superoxide dismutase and ascorbate peroxidase. The results presented in this study point out to the plasma membrane as the primary target for the short term production of activated oxygen species in response to Cd in BY2 tobacco cells followed by a coordinated activation of the antioxidant enzymatic system.