The influence of high-intensity pulsed electric field (HIPEF) parameters, namely, pulse frequency, pulse width, and polarity on tomato juice lipoxygenase (LOX) and hydroperoxide lyase (HPL) activities was studied using a response surface methodology. Samples were subjected to square-shaped pulses of 35 kV/cm for 1000 μs, with pulse width ranging from 1 to 7 μs at frequencies from 50 to 250 Hz, either in monopolar or bipolar mode. Tomato LOX was more resistant to HIPEF than HPL within the range of assayed conditions. An increase in frequency or pulse width resulted in a decrease of both residual LOX (RALOX) and HPL (RAHPL) activities. The lowest RALOX (81%) was observed when tomato juice was treated at 250 Hz for 7 μs in bipolar mode. Moreover, the same conditions led to the highest HPL activity reduction (RAHPL = 10%). A validation of the predictive models determined that 2nd-order expressions were accurate enough to fit the experimental results. ; This study was supported by theMinisterio de Ciencia y Tecnolog´ıa (Spain) through the Project ALI 2005-05768. This study has also been carried out with financial support fromthe Commission of the European Communities, Framework 6, Priority 5 “Food Quality and Safety,” Integrated Project NovelQ FP6-CT-2006-015710. I. Aguil´o- Aguayo thanks the Ministerio de Educaci´on y Ciencia (Spain) for the pre-doctoral grant.