In this paper, we address the problem of the interactive volume rendering of unstructured meshes and propose a new hardware-based ray-casting algorithm using partial pre-integration. The proposed algorithm makes use of modern programmable graphics card and achieves rendering rates competitive with full pre-integration approaches (up to 2M tet/sec). This algorithm allows the interactive modification of the transfer function and results in high-quality images, since no artifact due to under-sampling the full numerical pre-integration exists. We also compare our approach with implementations of cell-projection algorithm and demonstrate that ray-casting can perform better than cell projection, because it eliminates the high costs involved in ordering and transferring data.