A knife holder for a microtome has a plate arranged pivotably on its base member, which, in its functional position, covers the cutting edge of the knife and is spaced apart from the cutting plane towards the side of the knife holder remote from the specimen. The plate is also spaced apart from the knife holder on the side of the cutting edge of the knife. The plate precludes gripping of the cutting edge of the knife and a pivoting mechanism for the plate is coupled to a switch. When the plate is pivoted out of the functional position, the motor drive of the cutting movement is locked, or a brake precludes any movement of the knife slide or specimen slide. The plate preferably consists of a transparent material to permit observation of section removal in the functional position.