Simulated dynamic tests in shear on laminated rubber bearings are described. The purpose of the tests was to check the performance of the bearings when used as mounts for base isolating buildings against earthquake attack. Over 1,000 cycles were applied to the bearings, mostly at
 50% shear strain at a frequency in the range 0.2 to 0.9Hz. Values of damping were checked by carrying out separate torsional oscillation tests. It is concluded that the bearings are suitable for use in the dynamic mode for the purpose of achieving base isolation in earthquake resistant buildings. Damping is likely to be 2 to 3% of critical. Possibly greater values occur at faster speeds and under cold conditions. The use of separate lead or steel damping elements to prevent the build-up of damaging horizontal oscillations is considered necessary.