Biomechanical studies have shown that the distribution of stress and strain in biological tissue is strongly dependent on fibre orientation. Therefore, to analyze the local mechanical load, accurate data on muscle fibre orientation are needed. Traditional techniques to determine fibre orientation are inherently invasive. Here we used Diffusion Weighted MRI to non-invasively determine, in each image voxel of 0.23 x 0.23 mm, the diffusion tensor of water in the cat semimembranosus muscle. The direction corresponding to the largest eigenvector of this tensor was calculated. This direction was found to correspond qualitatively to the muscular fibre direction, as determined by visual inspection.