Healthy adult rabbit eyes were exposed to up to 4 h of continuous illumination with moderate light intensity, as is produced by the lamp of an ophthalmic operating microscope. Electroretinograms were recorded before and after the long period of illumination. The depression of the waves in the electroretinograms observed just following light exposure recovered within 1 h to normal values. Electron microscopy of the retina revealed changes within the cells of the pigment epithelium. These results are discussed in view of their clinical implications in human patients.