Abstract: An improved controlled-motion instrument is provided for grasping, holding or otherwise manipulating an object in operations such as endoscopic procedures. The instrument opens and closes jaws or other manipulation members by way of a longitudinally movable cam member, but maintains the longitudinal position of the manipulation members constant relative to the instrument's body regardless of opening and closing motion. The manipulation members thus have increased length-to-diameter ratio and column strength, and the cam provides positive lateral jaw support and stability during opening and closing. The movable cam member can also include other manipulation members thereon that work in conjunction with the longitudinally fixed manipulation members.