ABSTRACT. Bovine leukemia virus (BLV), the causative agent of enzootic bovine leukosis, is an exogenous, B lymphotropic retrovirus belonging to the Retroviridae family that induces persistent lymphocytosis in cattle and sheep. PCR has proven to be particularly suitable for investigating herds of cattle with a very low incidence of BLV infection and for clarifying doubtful serological results obtained by immunodiffusion or ELISA. The native Iranian and Russian cattle have a series of valuable traits that discriminate them as unique breeds that are well able to compete with western analogues. However, their gene pools have not been analyzed with molecular markers, including detection of BLV by PCR. Two pairs of primers were used: gag1 and gag2, and pol1 and pol2, which encompass 347-and 599-bp fragments of the BLV gene, respectively. Sixty-five Iranian Sistani, 120 Yaroslavl, 50 Mongolian, and 35 Black Pied cows were investigated. Among these 270 animals, we obtained 42 positive and 15 doubtful results in the first PCR. The second PCR was very effective in increasing BLV test reliability data to support detection of BLV.