The paper is devoted to development of the evaluation methods tor limiting condition of metal alloys and steels under uniaxial and biaxial proportional and non-proportional low-cycle fatigue. To investigate the fatigue behavior of Type 08X 18H I OT stainless steels and titanium alloys BT9 strain controlled tests under 12 proportional and nonproportional loading ar room temperature were carried out. A strain parameter. namely, a nonproportional strain range. is proposed to obtain a correlative dependence with lifetime. For the majority or the materials this dependence can be derived from uniaxial tests and described by a linear function. It made it possible to propose simple engineering method for lifetime prediction.