Adeno-associated virus is a member of the Parvoviridae family which are among the smallest and structurally simplest of the DNA animal viruses. The family Parvoviridae has been divided into three genera (Siegl et al., 1985): parvoviruses which can grown in dividing cells of vertebrates, densoviruses which multiply in insects and depen-doviruses which infect a broad range of vertebrates but usually require a co-infection with an adenovirus (Hoggan et al., 1966) for a productive infection in cell culture. Because of the frequent association with adenovirus stocks, the dependoviruses have been called adeno-associated viruses (AAV).