Lead-extrusion dampers are energy absorbing devices that have been designed to provide damping for seismic isolation systems. One type, called the constricted tube damper, has been manufactured for several applications in New Zealand. High manufacturing costs and some performance considerations associated with the damper led to consideration of an alternative design known as the bulged shaft damper. This report describes tests carried out on bulged shaft dampers of two sizes, 100kN and 700kN yielded force. Results show that the bulged shaft design of damper can be expected to perform well during major seismic events, including mainshock/aftershock sequences.