This paper describes a computer-controlled on-line testing hybrid system which performs the dynamic response analysis of layered sandy deposits. The basic concept of the operation is to solve the governing equations of motion by means of a step-by-step numerical integration scheme that incorporates the laboratory soil response in the numerical analysis. The feasibility of the approach is examined by comparing the results with the conventional numerical solutions and it is concluded that the on-line approach can adequately capture the essential features of the response of sandy soils under a seismic event.