An ostomy appliance comprising a front wall and a rear wall of flexible material forming a bag, the rear wall having an opening into the bag by which waste material can enter the bag and one of the walls has one or more vents through which gas may escape from the bag and having a filter covering said vent wherein gas inlet and outlet openings and provided in communication with a filter body, the arrangement being so that in use gas flows through the filter from the inlet opening to the outlet opening, such gas flow being confined to said filter body, wherein the gas inlet opening to the filter is provided with at least two separate and independent closed pathways having separated inlet openings communicating with the bag and separate and independent outlet openings communicating with the inlet opening of the filter, and wherein each of the outlet openings of the separate pathways are covered by a microporous membrane shows improved resistance against blocking of the inlet opening of filter.