A magnetic filter device for filtering ferromagnetic material from a fluid in which said material is suspended, has a pair of annular plates (5, 6) attached to either side of an annular magnet (2) of smaller diameter. Pairs of pole pieces (11, 12) radially disposed on the plates (5, 6) are aligned so as to generate fields of magnetic flux which promote the collection and retention of ferromagnetic material between the pairs of polepieces (11, 12).