Axial strain- and load-controlled fatigue tests of a 12Cr-2W ferritic heat resisting steel were performed at high temperatures to obtain a continuous fatigue life curve (S-N curve) over a wide range from 10(2) to 10(9) cycles using load-alignment adjusted testing machines. When the stress amplitude (sigma(a)) in the S-N curve was normalized by tensile strength (sigma(B)), the ratio (sigma(a)/sigma(B)) decreased to below 0.5 over 10(6) cycles at 650degreesC. The reason was considered to be caused by internal fractures over 10(6) cycles at 650degreesC. (C) 2004 Kluwer Academic Publishers.