A description is given of an endonasal filter including two essentially planar filtering components joined at their respective ends by a flexible element mounted, similar to a spring, across the cartilage between the two nostrils. The shape of the filtering components is that of a lunette as is the shape of the section at entry to the channel communicating with the nasal cavities. The filtering components are joined by a thin piece of plastic shaped to form a U-bend, the two parallel sides of which extend towards the filtering components on whose surfaces they assume the form of an oval that supports the component and to which it is made to adhere by application of heat.