Characteristics of pile forces induced by earthquakes are discussed from view points of the in ertia interaction due to the mass effect of a superstructure and the kinematic interaction due to the resistance effect of piles against soil motions. The numerical example indicates that the kinematic interaction effect should be properly considered in the seismic design of pile foundations. The practical method to evaluate the pile forces in the seismic design procedure is proposed. The method based on the static analysis of a single pile includes the new technic for relaxation of the fixity condition at the pile tip
