A system is provided for reducing restenosis. A catheter apparatus is provided with at least first and second mono-polar electrodes positioned at an inflatable balloon. The balloon is sized to be positioned and expanded at a restenosis site. A voltage pulse generator is coupled to the first and second mono-polar electrodes. The voltage pulse generator is configured to apply an electric field, in a controlled manner, to the restenosis site in an amount sufficient to produce electroporation of the restenosis site, and below an amount that causes thermal damage to the restenosis site.