I will describe a three-dimensional human-computer interface for neurosurgical visualization based on the bimanual manipulation of real-world tools. The user’s nonpreferred hand holds a miniature head that can be “sliced open” or “pointed to” using a cross-sectioning plane or a stylus held in the preferred hand. The nonpreferred hand acts as a dynamic frame-of-reference relative to which the preferred hand articulates its motion. I will also discuss experiments that investigate the role of bimanual action in virtual manipulation and in the design of human-computer interfaces in general.