This paper is concerned with a linear system whose transfer function can be represented by the gain constant, poles, and zeros, the parameters of the system. These parameters vary with time in an unknown manner. A scheme is presented in which these parameters are tracked. The system can be readily realized in terms of simple analogue components. The novel idea presented here lies in the fact that both poles and zeros of the unknown system are adjusted independently by the tracking system. Other similar schemes use fixed poles and adjustable gains.