• The clinical appearance, fine • ture, and permeability to horseradish peroxidase and fluorescein of subretinal neovascularization (SRN) in monkeys was correlated at various stages of vessel development: early (active leaking), intermediate (slightly leaking), and regressive (nonleaking). The degree of SRN permeability correlated well with the presence of endothelial cell fenestrations. The substantial changes in the fine structure and permeability of SRN during maturation can account for the different clinical manifestations. It is thus apparent that the time of morphologic correlation must be considered when studying a dynamic evolving process, such as SRN.