Ostomy bag with filter combination

An ostomy bag having a stomal aperture to receive a stoma in one wall of the bag and a gas venting aperture in the bag with a filter element covering the gas venting aperture, the bag including an intervening membrane 40, 52, 58 disposed between the front rear walls 12, 14 of the bag and between the stomal aperture and the gas venting aperture 30. The intervening membrane is liquid impermeable and gas permeable and supports an adequate flow rate of gas for ostomy bag applications. The intervening membrane preferably comprises a polytetrafloroethylene, microporous semi-permeable membrane laminated to a thermoplastic film layer which is heat sealable to the walls of the bag.