Human-computer interaction is one of the most important issues in research of Virtual Environments. This paper introduces interaction software developed for a virtual operating environment for space experiments. Core components of the interaction software are: an object-oriented database for behavior management of virtual objects, a software agent called virtual eye for viewpoint control, and a software agent called virtual hand for object manipulation. Based on the above components, some instance programs for object manipulation have been developed. The user can observe the virtual environment through head-mounted display system, control viewpoint by head tracker and/or keyboard, and select and manipulate virtual objects by 3D mouse.