Abstract: We present a simple and effective algorithm for ray tracing iso-surfaces of time varying data sets. Each time step is partitioned into separate ranges of potentional iso-surface values. This creates a large number of relatively small files. Out-of-core rendering is implemented by reading for each time step the relevant iso-surface file, which contains its own spatial subdivision as well as the volumetric data. Since any of these data partitions is smaller than a single time step, the I/O bottleneck is overcome. Our method capitalizes on the ability of modern architectures to stream data off disk without interference of the operating system. Additionally, only a fraction of a time-step is held in memory at any moment during the visualization, which significantly reduces the required amount of internal memory.