[en] High-cycle and ultrasonic fatigue data were obtained for Incoloy-800H and an attempt has been made to correlate them with available low-cycle data from the literature. Basic differences exist between the three test procedures since the first two involve load control at small amplitudes and high cyclic frequencies, whereas low-cycle testing involves strain control at higher amplitudes and slower strain rates. For tests in the range 70 to 1400⁰F it is shown that the low- and high-cycle fatigue curves may be correlated as a function of stress if the stable stress levels for the low-cycle experiments are taken to be the effective value. For correlations as a function of strain there is also good agreement between the low- and high-cycle data provided that the effective strains for the latter are obtained from cyclic stress-strain curves. Stress-to-strain conversions by the use of Young's moduli are not acceptable since they do not take into account the plastic deformation which occurs during straining. For ultrasonic fatigue the endurance limit at 1100⁰F is much lower than the value for high cycle testing. The lower limit is probably associated with very local plastic deformation which possibly causes sub-surface crack initiation