We investigated whether newly developed virtual 3D environments (VEs) based on a modification of the computer game Quake III Arenao are suitable for psychological experimenting. Internal validity of data collected in VEs may be threatened due to a priori individual differences in general performance in VE navigation and in susceptibility to cybersickness. The main question was whether individual differences in performance can be diminished by means of training. Additionally, the susceptibility of different subsamples to cybersickness when rnoving within VEs was examined. 85 participants took part in an experiment where they had to fulfill simple tasks in three VEs. Navigation performance was measured as the time participants needed to make their way through the VEs. Differences in navigation performance between different levels of experience were diminished by training, indicating that internal validity can be obtained. A classification tree reveals that game-inexperienced female participants aged over 31 years have the highest risk of experiencing cybersickness. VEs based on modifications of computer games seem to be an extremely promising and inexpensive possibility for the administration of psychological experiments.