Bovine leukemia virus (BLV) propagated in a cell clone of fetal lamb kidney origin was transmitted by cell contact to different mammalian cells including human cells. The transmission of the BLV genome was effectively achieved by cocultivation of mitomycin-C-killed, virus-producing cells of the cell clone with recipient cells. In particular, human cells of neural origin were highly susceptible to BLV infection, while some other cells were resistant. The transmission of the BVL genome from virus-nonproducing cells failed which suggests the existence of virus specific receptors on the cells. The donor cells contained three integrated BLV proviruses. In recipient cells only one provirus was found. The majority of cells contained both unintegrated and integrated BLV provirus. In the cells containing the transmitted BLV, the viral genome was expressed to its protein products. The results indirectly suggest that retroviruses with similar properties could cause various neural diseases in man.