Intermittent stabilization of a load table supported by pneumatic vibration isolators is provided by determining a load shift condition, increasing passage of gas to the pneumatic vibration isolators and imposing external or internal damping on the load table in response to that load shift condition. For internal damping, the pneumatic vibration isolator is provided with damping fluid in one of its pneumatic chambers and a damping fluid friction passage is provided between that damping fluid in that one pneumatic chamber and the other pneumatic chamber.