Abstract
Virus particles released from chick embryo cells infected with equine influenza virus at high multiplicity in the first 10 hr after infection contained the complete RNA component of infectious virus. Virus released later (20 to 30 hr after infection) was of von Magnus type and contained the RNAs of incomplete virus. It is concluded that the formation of von Magnus virus in chick embryo cells is due to a defective synthesis of virus RNA components and not due to a defective assembly and release of virus particles.