The receptive field (RF) orientation of 53 simple visual cortical neurons was determined by recording the activity of single cells during presentation of stationary bars of light. An RF tuning curve was constructed for each cell by averaging the neural discharge resulting from the repeated presentation of a number of slit orientations. RF curves were then determined again, following a 45 degrees roll tilt of the entire head and body, and subsequently after the return of the animal to the original horizontal position. RF tuning curves were typical of what others have found to characterize simple cells, and were highly replicable on the return to the starting position. In 73% of the cells studied, the RF orientation after tilt remained unaltered relative to the head axis (+/- 15 degrees); in the remaining 27% of the cells RF orientations either under- or over-shot the retinal tilt by more than 15 degrees, and in some cases by as much as 45 degrees. These results support the hypothesis that the well documented vestibular inputs to visual cortex play a role in modifying the RF orientation selectively of visual cortical neurons, and suggest that such information may be an important neurophysiological substrate underlying visual spatial constancy mechanisms.