The present study confirms the introduction of bovine leukaemia virus (BLV) into Egypt. During an outbreak of exotic bovine leukosis among an imported cattle herd in Arab El-Aoumar dairy farm, Assiut Governorate, Upper Egypt, serological screening was done in the farm using agar gel immunodiffusion test which indicated that 206 (46.8%) out of 440 tested cattle were serologically positive. Bovine leukaemia virus particles were detected in leukocyte cultures and milk of seropositive cattle selected from the imported BLV-infected herd. The virus particles were demonstrated in leukocyte cultures of 48 animals and in milk samples of 39 seropositive milking cows. Phytohemaggultinin was added as culture stimulant to 10 out of 48 leukocyte cultures. In leukocytic cultures, the detected virus particles were 90-120 nm in diameter with centrally located electron dense nucleoid about 60-90 nm in diameter. Phytohemaggultinin-stimulated cultures produced more viruses per cell than did cultures without mitogen. In milk samples virus particles were detected in resuspended milk pellets by negative staining electron microscopy and in ultrathin sections of milk pellets by transmission electron microscopy. The most observed post-mortem findings of dead and culled cattle were enlargement of the lymph nodes which also contain tumour lesions on cut sections. Similar hyperplastic lesions were seen in the spleen and Peyer's patches. We suggested that caution should be taken with milk from BLV-infected cows as the milk contains free BLV particles. This study agument our previous published paper which reported that the imported Holestein Freisian cattle herd from Minnesota, USA into Upper Egypt was infected with bovine leukaemia virus, and should be completely eradicated to avoid spreading of the infection to other localities in Egypt