We have studied the infection by the bovine immunodeficiency-like virus (BIV) in three experimentally infected calves, by polymerase chain reaction (PCR) and reverse transcription-polymerase chain reaction (RT-PCR), from the peripheral blood mononuclear cells (PBMC). Two primer pairs located in thegag andpol regions of the viral genome allowed to detect the viral genomic DNA by PCR, as well as the unspliced genomic viral RNA transcript, by RT-PCR. We also present the evidence of the presence in peripheral blood mononuclear cells (PBMCs) of a mRNA transcript of the regulatorytrans-activatortat gene, according to the splicing pattern of the viral genome, by use of reverse transcription followed by nested PCR. The active expression of the virus in these animals was further assessed by the sequential rescue of the virus from unstimulated PBMCs in cell culture, from 4 weeks until 15 months following the infection.