The quasisteady-conduction-current density in polythene film at room temperature has been measured with the applied stress varying between about 0.1 MV/cm and 1.2 MV/cm and with film thicknesses between 25 μm and 200 μm. The current density at constant applied stress was found to be independent of the specimen thickness. It is also shown that the conductivity of polythene film can be greatly increased, and its electric strength appreciably reduced, by an oxidation treatment that produces carbonyl and nitrogroups in the molecular chains.