Ultrastructural examination was performed on 30 eyes selected on the basis of a light microscopic classification as representing all stages of macular degeneration. The eyes belonged to 29 patients aged 40 to 91 years at death and all patients with the exception of the 40-year-old had been examined during life. The results indicate that monocytes, lymphocytes, fibroblasts and mast cells may play a role in the formation of breaks in Bruch's membrane at early and late stages of macular degeneration. The implications of these observations are discussed in the context of their possible role in choroidal neovascularization.