Abstract: An apparatus is provided for holding down membrane elements in respective wells of a multiwell plate, which has, at its top side, respective openings of the respective wells. The apparatus has, at its upper region, a support structure having respective openings, and respective corresponding retention elements which extend downwards from the respective openings of the support structure, so that respective retention elements protrude into respective wells when the support structure has been placed onto the top side of the multiwell plate. A retention element has multiple webs which extend downwards from the support structure and the ends of which are connected to one another at a bottom side of the apparatus by means of a connection element.