The object of the research was to identify role of functional nervous asymmetry in formation of pathology in experimental animals. The role of functional asymmetry of the brain hemispheres in development of ectromelia and melanoma at (CBAxC57BL/6)F1 mice was investigated. It has been established, that mice with domination of motor functions in the left hemisphere ("right-handed") are more resistant against infection with ectromelia virus, and melanoma B-16 grows more slowly in these mice as compated with animals with domination of motor functions of the right hemisphere ("left-handed"). Hence, for the first time the role of functional nervous asymmetry in pathogenesis of ectromelia and melanoma (B-16) in mice (CBAxC57BL/6)F1 is established.