Bovine syncytial virus (BSV) was isolated from direct cell culture of tissues obtained from 2 adult cows, from buffy coat cells from a third cow which were co-seeded with bovine fetal spleen (BSp) cells, and from direct cell cultures from a 5 month old bovine fetus obtained from a slaughter house. The viral isolates were extremely cell-associated, produced very low titers in cell cultures, and were labile to chloroform, heat, and freezing. Electron microscopy of infected cells revealed intracytoplasmic foci of discrete double membrane bound viral particles approximately 135 mμ in diameter. Speculation is presented that 2 types of syncytial viruses exist in cattle—the cell associated viruses reported from the United States and Britain which as yet have not been associated with disease, and the bovine respiratory syncytial viruses isolated from respiratory outbreaks in Europe and Japan.