To investigate the neural substrates for the perception of motion and of position in depth, we examined the changes in regional cerebral blood flow during positional and motion stereopsis in humans by positron emission tomography. During positional stereopsis, the right striate and peristriate cortices (areas V1/V2 and V3) and the inferior parietal lobule were significantly activated. During motion stereopsis, the right striate and peristriate cortices (V1/V2) and the ventrolateral occipital cortex (V5) were significantly activated. These results suggest that brain regions active during stereopsis may be dependent, despite their considerable overlap, on the properties of stereopsis, i.e. positional or motion stereopsis.