Bovine leukemia virus (BLV) is a deltaretrovirus that infects and induces accumulation of B-lymphocytes in the peripheral blood and lymphoid tissues of cattle, leading to leukemia/lymphoma. BLV can also be experimentally transmitted to sheep, in which disease appears earlier and at higher frequencies. Abnormal accumulation of leukemic B-lymphocytes results from an alteration of different parameters that include cell proliferation and death as well as migration to lymphoid tissues. Interestingly, B lymphocyte turnover is increased in BLV-infected sheep but reduced in cattle, revealing a potential relationship between cell kinetics and disease progression.