SUMMARY Chicks, half of which were inoculated with infectious bursal disease virus (IBDV) at 1 day old, were inoculated 1, 2, 3, or 4 weeks later with chicken anemia agent (CAA). Chicks inoculated with CAA alone at 2 weeks of age or later did not have anemia. The chicks inoculated with IBDV and also with CAA 2, 3, or 4 weeks later developed anemias; some of them died. Uninoculated one-day-old chicks reared in contact with chicks inoculated with CAA alone, and chicks inoculated with IBDV alone at 1 day old did not have anemia, but they did when reared in an isolator together with chicks inoculated with IBDV and CAA, or CAA, or in an isolator environmentally contaminated with IBDV and CAA. Chicks infected dually with IBDV and CAA exhibited essentially the same clinical signs and lesions as chicks inoculated only with CAA at 1 day old.