Images taken with the two ultraviolet cameras on board the Viking spacecraft were examined for evidence of transient decreases of Earth's ultraviolet dayglow. Comparison of near-limb observations of day-glow intensities with those at smaller angles to the nadir with the camera sensitive to OI 130.4 nm emissions supports the existence of transient decreases in the near-nadir dayglow. However, the amount of near-nadir imaging is severely limited and only several significant events are found. More decisive confirmation of the existence of such transient decreases must await a larger survey from another spacecraft. The diameters of these regions as detected with Viking are ~50 to 100 km. Occurrence frequencies, intensity decreases, and dimensions for these clusters of darkened pixels are similar to those previously reported for such events, or 'atmospheric holes', as seen in images of the ultraviolet dayglow with Dynamics Explorer 1. ¿ American Geophysical Union 1989