Previous genealogic studies of Leber's disease have focused on affected individuals with optic atrophy. Despite its diagnostic importance, peripapillary microangiopathy has not been widely recognized. In our study, the genealogic evaluation includes asymptomatic subjects with microangiopathy. Another new aspect is a genealogic analysis of the cardiovascular abnormalities found in members of families with Leber's disease. Our results suggest that every daughter and son of a female carrier inherits the trait, thus satisfying the criteria for a maternally inherited disease. Microangiopathy, without optic nerve dysfunction, probably represents the mildest stage of the disease. The high frequency of electrocardiographic abnormalities in the off-spring of the female carriers suggests an important link with Leber's disease.