In this work, to render at least 512³ voxel volumes in real-time, we have developed a sort-last parallel volume rendering method for distributed memory multiprocessors. Our sort-last method consists of two methods, Hsu?s segmented ray casting and our divided-screenwise hierarchical (DSH) compositing, in which each processor produces a subimage and merges all the produced subimages into the final image. This paper describes the DSH method, which aims at achieving high performance compositing on a large number of processors. Our implementation on a 64-node PC cluster can composite a 512² pixel image about twice as fast as an existing method, the binary-swap method, so that can render a 512 x 512 x 224 voxel volume at approximately eight frames per second (fps).