Rod photoreceptors can be saturated by exposure to bright background light, so that no flash superimposed upon the background can elicit a detectable response. This phenomenon, called increment saturation, was first demonstrated psychophysically by Aguilar and Stiles and has since been shown in many studies to occur in single rods. Recent experiments indicate, however, that rods may be able to avoid saturation under some conditions of illumination. We now show in ex vivo electroretinogram and single-cell recordings that in continuous and prolonged exposure even to very bright light, the rods of mice from both sexes recover as much as 15% of their dark current and that responses can persist for hours. In parallel to recovery of outer segment current is an approximately 10-fold increase in the sensitivity of rod photoresponses. This recovery is greatly decreased in transgenic mice with reduced light-dependent translocation of the G protein transducin. The reduction in outer-segment transducin together with a...