Abstract: The invention relates to plastic packing for biological treatment of fluids, comprising a series of plates packed without the use of adhesive, provided with convex and concave ribs wherein inclined channels with corrugated side-walls are arranged between the adjacent sheets. The sheets are formed by M-profiles, the joining lines and centerlines of the M-profiles are unbroken in the full height of the packing and are at a maximum 30.degree. to the vertical, furthermore the corrugated parts are ribbed surfaces formed only on the shanks of the M-profiles, so that a flat strip without ribs is on both sides of the joining lines of the profiles. According to one of the versions, the plastic sheets are joined opposite each other, so that the shanks of M-profiles end in a point of junction.