This paper considers the problem of approximating a continuous-data system by a sampled-data model. The approximation is achieved by comparison of the states of the systems at each sampling period, It is shown that it is possible to match all the states if a hold device of sufficiently high order is utilized after the sampler. The order of the hold device necessary depends on the ratio of the number of states and the number of controls of the system. An example is presented to illustrate the procedure. The method is useful when an existing analogue system is to be converted into a digital system with minimal changes in performance.