Chicken anemia (CAA) is a novel avian virus which recently been identified. It produces aplastic anemia in young chicks on an experimental basis. It may presumably be a major causative agent of anemic diseases in field chickens. CAA fails to grow under a standard avian cell culture. It propagates, however, in some lymphoblastoid cell lines established from lymphomas of chickens. These cell lines are used to isolate and titrate CAA, and also to detect the antibody to CAA. Owing to the development of an assay system in vitro, knowledge on CAA has been accumulated rapidly.