The leukocytic formulae of the peripheral blood of Vipera berus (Linnaeus, 1758) from the Samara region (Samara City) and Vipera renardi (Christoph, 1861) from the Saratov region (Khvalynsk district) were studied. Some features of the leukocytic blood composition of the species studied were revealed, manifested by the predominance of a specific component in the immune reactions of Vipera berus, in comparison with Vipera renardi.