[en] High temperature creep-fatigue design rules already established in the ASME and RCC-MR codes have been reviewed, analysed and reformulated for the assessment of components built from EUROFER 97. For the verification of the rules isothermal two-steps fatigue, thermo- mechanical fatigue and isothermal multiaxial fatigue tests have been performed and evaluated. It has been found that the conventional design rules are not straightforward applicable for EUROFER 97. They can not cover the strong lifetime reduction observed under thermo-mechanical and multiaxial cyclic loadings which has been mainly attributed to the different cyclic softening behaviour under these loading modes in comparison to isothermal uniaxial loading. Hence, the rules have been modified by deriving new fatigue design curves taking into account cyclic softening effects. Thereby, a damage model recently developed to describe the deterioration of EUROFER 97 under creep fatigue loading has been used. Even the improved rules have been sufficiently conservative when considering the verification tests performed further verifications are recommended. (orig.)