We have discovered a new type of abortive replication in Vero cells infected with fowl plague virus. In these cells there is an enhanced splicing of the colinear mRNAs of segment 7 and presumably also of segment 8, leading to an extreme overproduction of M2 and NS2 proteins. The cleavage of the hemagglutinin (HA) into HA1 and HA2 and the processing of its carbohydrate side chains are markedly retarded and incomplete. Although some of the HA is incorporated into the plasma membrane, leading to a positive hemadsorption, most of it accumulates in a discrete compartment close to the nuclear membrane, representing presumably the reticuloendothel and/or the Golgi network. Neuraminidase activity in Vero cells is extremely low. The nucleoprotein is normally released from nuclei late in infection. Very little infectious virus is released, and its spread is highly impeded.