Cultures from pig bone marrow cells were infected with ASFV and the replication cycle was studied. In the cytoplasmic replication areas there are a differentiation of membrane segments. Some of them are polygonal, which give rise to virus particles. An over production of viral coded materials, including non-polygonal membranes seems to be an important feature of the replicative cycle of ASFV in this cell system. Viruses are released enveloped with a cellular membrane. Paracrystalline arrays of viruses are seldom seen in the cytoplasm. At no time did we see viruses in the nucleus. Infected cells showed marked cytopathic effect, beginning at early times post infection.