Results are presented showing that Ca++-activated endogenous phospholipases are able to catalyze hydrolysis of hydroperoxydiacyglycerophosphatides with subsequent formation of monoacyglycerophosphatides and free hydroperoxides of fatty acids in frog rod outer segment membranes. The role of endogenous phospholipases in the mechanisms of repair of photoreceptor membranes subjected to lipid peroxidation, as well as in "molecular substitution" of phospholipids under membrane renewal is discussed.