A filter and gas vent system incorporated in an ostomy bag during its manufacture includes a filter in the shape of a flat band, its deodorizing core being left open to the ambient air at two ends of the filter. The latter is held inside the bag by two weld seams joining walls of the bag to each other. A key feature of the invention is that each of the two weld seams extends from one of two side edges of the bag to its upper edge. The filter can thus be contained entirely in the bag, which thus isolates the ends from the outside. The material from which the core of the filter is made, often activated charcoal, no longer risks soiling the clothes or being driven off when the subject is showering. This invention also prevents the liquid matter collected in the bag from seeping out by passing along the core of the filter.

A vent device, in particular for a stoma bag, constituted by an essentially flat housing comprising a base having a face inside the housing and a face outside the housing, and adapted to be fixed via said outside face to an exposed face of said bag and provided with an opening communicating with said bag, and also provided with a valve of the type that is closed at rest, the valve being formed by a valve member adapted to bear against the inside face of said opening in said base, and being integral with resilient means for urging said valve member against said base with a predetermined return force, wherein the housing further includes a removable cover adapted to close said base and wherein the valve member is secured to said cover.