SUMMARY Studies of nonspecifi c adaptation responses of organism (NAR) and blood composition were performed on white rats in conditions of single physical load, variable by length. It has been shown that in course of the load of maximum length, the organism undergoes all stages of stress that is proven by motor disturbance, the blood composition changes and decreasing of the level of NAR. It has been shown that the stress level of the physical work in unusual conditions mostly depends on the length rather than on the intensity of load.