Brain-computer interfaces (BCIs) provide a novel form of human-computer interaction. The purpose of these systems is to aid disabled people by aording them the possibility of communication and environment control. In this study we present experiments using a P300 based BCI in a fully immersive virtual environment (IVE). P300 BCIs depend on presenting several stimuli to the user. We propose two ways of embedding the stimuli in the virtual environment: one that uses 3D objects as targets, and a second that uses a virtual overlay. Both ways have been shown to work eectively with no signicant dierence in selection accuracy. The results suggest that P300 BCIs can be used successfully in a 3D environment, and this suggests some novel ways of using BCIs in real world environments.