In volume rendering, transfer functions are used to map voxel property into color and opacity. The most common voxel property used in transfer functions is the voxel intensity. Multiple voxel properties can also be used, and we then get a multidimensional transfer function.In this thesis, we want to test how well a two-dimensional transfer function performs, compared to a transfer function of just one dimension. To test this, we have implemented a fast volume rendering application using GPU shader programming. We got a radiologist, a surgeon and a computer engineer to evaluate our application using both one and two-dimensional transfer functions on different datasets. The test shows that a transfer function of both voxel intensity and gradient magnitude is better than a transfer function of just intensity for reducing noise in the rendering. The test also shows how difficult manual transfer function manipulation can be.