This study investigated the effects of high pressure processing (HPP) on the barrier properties of eight multilayer films. Pouches made from these films were filled with distilled water, sealed and then pressure processed at 600 and 800 MPa for 5, 10 and 20 min at 45 degreesC. Controls were similarly prepared but exposed to atmospheric pressure. After processing, all pouches were dried and their oxygen, carbon dioxide and water vapour permeance determined. Films used in this study were PET/SiOx/LDPE, PET/Al2O3/LDPE, PET/PVDC/nylon/HDPE/PE, PE/nylon/EVOH/PE, PE/nylon/PE, metallized-PET/EVA/LLDPE, PP/nylon/PP and PET/PVDC/EVA. Results showed that metallized PET was most severely affected by HPP, as its permeance values for oxygen, carbon dioxide and water increased as much as 150%. Copyright (C) 2000 John Wiley & Sons, Ltd.