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The finite difference time domain (FDTD) method is well suited for the computation of bio-electromagnetic effects and has become the method of choice for most researchers in this area. There does however remain some limitations on its use. Firstly the FDTD method requires large amounts of memory and computational power. The size of the model is dependent upon both the physical size of the model and its resolution. Higher frequencies of operation require higher resolutions. This can place the solution of some problems outside the capabilities of the technique. Secondly the representation of the problem (i.e. the head and the telephone) can cause some difficulties. Often the telephone has to be represented by a series of boxes which approximate the shape of the actual device. The paper addresses these two problems. The problem size is accommodated by the use of a parallelized version of the FDTD method, which is run on large parallel processing machines such as the IBM SP-2. Additionally a method of inputting data from the computer aided design (CAD) files of the telephone has been developed. These two techniques are used in combination with two head models which have been developed from MRI images of two human subjects. The usefulness of the techniques developed and comparisons of the specific absorption rates (SARs) in the two models is discussed.