For the development of DNA diagnostics of animal infections, we adopted the amplification and detection of bovine leukosis proviral DNA by polymerase chain reaction(PCR) and enhanced chemiluminescence(ECL) technique performances as a model system. The PCR technique is an in vitro method in which genomic or cloned target sequences are specifically and enzymatically amplified as directed by a pair of oligonucleotide primers. So, the PCR technique is an excellent rnethod to address the issues of sensitivity and specificity in the characterization of nucleic acids. The fact that the PCR technique allows the specific amplification of discrete fragments of DNA makes it much easier to detect nucleic acid fragments that are initially present in the sample in picogram quantities. The ECL gene detection systern is also a novel sensitive, non-radioactive system for the detection of nucleic acid hybridized on both nylon or nitrocellulose membranes. It is characterized by direct labelling of probe sequences with horseradish peroxidase(HRP) combined an ECL detection reaction: the light output is captured on bluelight sensitive film. Bovine leukosis virus(BLV) is considerably distributed in cattle herds. It infects B lymphocytes and causes neoplastic disease with various levels of infected animals. Direct economic losses are incurred as a result of death, reduced milk production and condemnation at slaughter. Thus, the iden- tification of cattle infected with BLV is of significant concern to the cattle industry. For this reason, PCR amplification and ECL gene detection systems were applied to examine cattle for the presence of BLV proviral DNA in peripheral blood mononuclear cells(PBMC). BLV sequences were detected in 15(10.2%) of 147 dairy cattle examined (30 Korean cattle were all negative) by PCR-ECL system. Syncytium assay by in vitro cocultivation rnethod has showed 12 of 15 PCR-positive samples. These findings indicate that PCR-ECL is a sensitive method for the detection of BLV in cattle. Thus, in principle, these methods are easily applicable not only to the DNA diagnosis of BLV, but also to the DNA diagnosis of other microorganisms including various viruses.