The McGurk effect or fusion illusion, in which mismatched auditory and visual speech sound components are perceived as an emergent phone, is extensively used in auditory-visual speech perception research. The usual method of running experiments involves time-consuming preparation of dubbed videotapes. This paper describes an alternative, the Computerised Auditory-Visual Experiment (CAVE), in which audio dubbing occurs on-line. Its advantages include reduced preparation time, greater flexibility, and on-line collection of response type and latency data.