The problem associated with the determination of earthquake forces on equipment in nuclear power plants is explored. The response of equipment on the ground is determined using the well-established methods for structures. The response of equipment on structures, being mainly a function of the natural frequencies of the supporting structure, is very sensitive to slight variations of the structure frequencies. The assumption of modal analysis and proportional damping grossly overestimate the forces on equipment located on the foundation when soil-structure interaction effects are considered. To obtain more realistic responses nonproportional damping and, therefore, direct integration techniques should be used for the solution of the differential equations. A testing program should be initiated when analyzing complicated equipment. Scaling laws can be very useful in overcoming limitations of shaking equipment. Effects of nonlinearities can also be adequately studied.