The authors propose a new criterion of predicting the rate of crack growth in biaxial loading based on analysis of the local stress-strain state of the crack tip, the size of the plastic zone, and the plasticity margin of cyclic failure. The derived calculation dependences are compared with the experimental data obtained by the authors and other investigators. The results are in satisfactory agreement as a result of taking into account the effect of the load level, the properties of the material, and the biaxial loading.