The invention relates to a holder for holding a carrier, wherein the holder is inserted into a cylinder-shaped well, for example, of a multiwell plate. In addition the invention relates to a multiwell plate with such a holder. In order to provide a possibility for the reliable support of a carrier in a holder, wherein the holder ensures a secure and specified positioning of the carrier in a well and reliably prevents the carrier and the holder from falling out of the well, a holder is proposed for insertion into a cylindrical well and to support the carrier. The holder comprises a support, a holding piece and a connecting piece which connects the supporting piece with the holding piece, wherein the holder together with the lateral external surfaces of the supporting piece, the holding piece and/or connecting piece lies against at least one lateral internal surface of the well, and wherein the carrier is inserted on the support and under the holding piece.