Assembly method for a microsurgical instrument, which has a proximal handle mechanically connectable to a hollow shaft, which shaft can be coupled releasably to a tool head via a bayonet connection, wherein the handle has at least one actuation device, which can be operatively coupled to an actuation rod that can be guided in the shaft, wherein the bayonet connection has two bayonet elements (3, 4) with respective longitudinal slits (312, 43) which are aligned in a locked state of the bayonet connection, and at least one longitudinally movable cam is guided axially in the longitudinal slits (312, 43), and wherein the actuation rod can be inserted with its proximal end portion into the handle and has at least one flattened part, which can be engaged by at least one clamping block arranged on the handle in a fixed position with respect to the longitudinal axis, wherein a sleeve connected releasably to the shaft is provided in order to be connected to the handle for conjoint rotation and movement therewith, and the actuation rod can be guided in the sleeve, and wherein, in order to lock the axial movement of the sleeve with respect to the handle, the sleeve has a circumferential groove that can be brought into engagement with one or more corresponding engagement means of the handle, while, in order to secure the degree of freedom in rotation, grooves extending along the longitudinal axis are provided in the distal end portion of the sleeve, said method comprising the steps of: a) making available the handle, the hollow shaft and the tool head, with the actuation rod operatively coupled thereon, b) pushing the shaft, with a bayonet element (3, 4) at the front, over the actuation rod and bringing the bayonet element (3, 4) of the shaft into engagement with the other bayonet element (3, 4), c) rotating the shaft and the tool head relative to each other until the bayonet connection is in the locked state, thereby also aligning the longitudinal slits (312, 43) of the bayonet elements (3, 4), d) inserting the proximal end portion of the actuation rod into the handle, thereby engaging the flattened part of the actuation rod with the clamping block of the handle and securing the actuation rod against rotation relative to the handle, e) mechanically connecting the handle to the sleeve, f) moving the cam into the longitudinal slits (312, 43) and forming an anti-rotation means near the tool. a) making available the handle, the hollow shaft and the tool head, with the actuation rod operatively coupled thereon, b) pushing the shaft, with a bayonet element (3, 4) at the front, over the actuation rod and bringing the bayonet element (3, 4) of the shaft into engagement with the other bayonet element (3, 4), c) rotating the shaft and the tool head relative to each other until the bayonet connection is in the locked state, thereby also aligning the longitudinal slits (312, 43) of the bayonet elements (3, 4), d) inserting the proximal end portion of the actuation rod into the handle, thereby engaging the flattened part of the actuation rod with the clamping block of the handle and securing the actuation rod against rotation relative to the handle, e) mechanically connecting the handle to the sleeve, f) moving the cam into the longitudinal slits (312, 43) and forming an anti-rotation means near the tool.