A brief review of the literature covering the perception of flicker is followed by a description of experiments to investigate flicker mechanisms, using a VDU with a light background and with a minimum refresh rate of 70 Hz. A previous hypothesis that there is a link between scan-line direction and perception of flicker was not upheld, although there was support for the view that 70 Hz may not be a high enough refresh rate to ensure freedom from flicker in large displays.