Viral leukemia of cows is a chronic infectious disease characterized by neoplasia of hematopoietic tissue. The agent of disease BLV is found in infected lymphocytes as a provirus. The infected lymphocyte is not destroyed in the susceptible organism. The goal of our research is comparison of the structural and functional state of the cytoskeleton of lymphocytes of healthy and BLV-infected cattle using the method of atomic force microscopy. It was found out that the surface of healthy lymphocytes is smoother, their average volume is 21.5 % bigger and Yung’s module is 37% higher than those of the infected cells. So, membranes of lymphocytes of BLV-infected cattle are characterized by increased rigidity with less elasticity.