In this paper, the effects of the asynchronous ground motion on frequency contents and amplitudes of hydrodynamic pressures are investigated considering dam-reservoir-foundation interaction. The behaviour of the dam, the reservoir and the foundation is expressed in terms of the displacements (Lagrangian approach) in the formulations obtained using finite element method. Hydrodynamic pressures are calculated for various earthquake wave velocities. It is observed that asynchronous ground motion affects the frequency contents of hydrodynamic pressures slightly. However, the amplitudes of the hydrodynamic pressures decrease considerably when asynchronous ground motion is taken into account. (C) 1998 Elsevier Science Ltd and Civil-Comp Ltd. All rights reserved.