Exposure of isolated frog rod outer segments to light (5000 lux) induces membrane disorganization and swelling. An increase of about 50% on lipid peroxidation, measured by the extent of malonaldehyde formation, accompanied the light-induced damage. Taurine and hypotaurine (25 mM) prevented the increase in lipid peroxidation, and provided an entire protection of rod outer segment structure.