A new technique based on the use of supercritical carbon dioxide (CO2) for cleaning HEPA filters was developed. Glass fiber filters and polytetrafluoroethylene (PTFE) membranes loaded with dioctylphthalate (DOP) droplets were cleaned with supercritical carbon dioxide under various conditions. The cleaning performance was evaluated by the weight recovery of the filter media and the recoveries of their collection efficiencies and pressure drops. The extent of DOP removal from glass fiber filters was nearly complete with supercrifical carbon dioxide cleaning at 20 MPa and 40 degreesC for a period of 120 min and the collection efficiency and pressure drop were also recovered to those of new filters. Furthermore, thenno-gravimetric (TG) analysis showed that cleaning did not wash away any of the binder resins. However, less satisfactory results were obtained for PTFE membrane filters. (C) 2004 Elsevier B.V. All rights reserved.