Abstract: In surgery, especially in microsurgery, anastomosis, consumes a considerable part of the time. In order to carry out anastomosis rapidly and reliably a surgical instrument (1) according to the invention is provided with two clamping means (2,3), each being arranged to support a fastening means (5a,5b) consisting of a ring with axially directed pins (6). The clamping means (2,3) are rotatably connected to the instrument and can be actuated by a mechanism (i.a. 7) to be turned towards each other to join the fastening means (5a,5b) and vessels or organs (50,51) threaded onto these.The invention relates to fastening means (5a,5b) shaped in such a manner that they are retained in the clamping means (2,3) of the instrument until the joining is accomplished.