The aim of the present study was to follow out the alterations in some haematological and blood biochemical parameters in cattle spontaneously infected with enzootic bovine leukosis virus with regard to the invivodifferentiation of bovine leukosis stages. The experiment included 76 cows at various ages and body weight. Serological leukosis tests were done by agar-gel immunodiffusion test with a commercial kit of Synbiotiсs (France), containing standardised gp 51 antigen and positive serum approved by the EU. On the basis of haematological results, the cows were divided into three groups: first group – EBL-seropositive with normal haemogramme; second group – EBL seropositive with altered haemogramme and third group – controls. In cows from the first and the second group, a statistically significantly increased blood cell counts was established compared to healthy controls. The total WBC were increased in the second group (leukocytosis) up to 33.21×109/l vs reference range of 5-10×109/l as well as lymphocyte percentages (lymphocytosis) – 81.89% (reference 40–63%). A reduction in the proportion of neutrophils to 12.78% (relative neutropenia) vs the reference range of 22-49% and monocytes (monocytopenia) to 1.78% (reference range 2–6%) was observed. A statistically significant reduction in Ca concentrations (4.41 mg/dl) and higher inorganic phosphate levels (5.28 mg/dl) were established in cows from the second group. Also, ASAT activity was considerably lower – 47.03 U/l, while alkaline phosphatase increased slightly within the reference range up to 167.68 U/l and 165.81 U/l in groups one and two, respectively. The present haematological and whole blood/serum biochemical results in cows spontaneously infected with EBL virus could be used as prognostic markers of the course of the disease, to distinguish the stages of infection with regard to alive diagnostics.