Abstract: We present occlusion-switches for interactive visibility culling in complex 3D environments. An occlusion-switch consists of two GPUs (graphics processing units) and each GPU is used to either compute an occlusion representation or cull away primitives not visible from the current viewpoint. Moreover, we switch the roles of each GPU between successive frames. The visible primitives are rendered in parallel on a third GPU. We utilize frame-to-frame coherence to lower the communication overhead between different GPUs and improve the overall performance. The overall visibility culling algorithm is conservative up to image-space precision. This algorithm has been combined with levels-of-detail and implemented on three networked PCs, each consisting of a single GPU. We highlight its performance on complex environments composed of tens of millions of triangles. In practice, it is able to render these environments at interactive rates with little loss in image quality.