A scalpel has a handle (1) and a blade carrier (2) movable within a longitudinally extending cavity therein between an operative position in which a blade (5) on the blade carrier is exposed for use and an inoperative retracted position. A manually operable slider (4) moves the blade carrier (2) that has a catch face (21) directed rearwards in the operative position. The catch face partially aligns with a stop face (22) provided on the handle (1) in the normal operative position of the blade carrier such that force exerted on a blade carried by the blade carrier in the direction of the length of the handle causes engagement of the catch face with the stop face to arrest movement of the blade carrier into the cavity. Transverse biasing of the blade carrier (2) is overcome by pressure exerted on the slider (4) to retract the blade carrier (2) into the handle with the catch face (21) passing the stop face (22).