The low-cycle fatigue (LCF) behavior of Waspaloy was studied in uniaxial and torsional loading for two heat treatments at 24 and 649°C. It was shown that for both heat treatments deformation and failure mechanisms were independent of stress state at 24°C. Deformation occurred by precipitate shearing and the formation of intense shear bands for the coarse-grain/small-precipitate (CG-SP) condition and by precipitate looping and loosely defined shear bands for the fine-grain/large-precipitate (FG-LP) condition. Failure in both microstructures was associated with the formation of shear cracks. At 649°C deformation and failure mechanisms for the FG-LP condition were independent of stress state, and the mechanisms were similar to those observed at 24°C. For the CG-SP condition, the situation was different. Failure occurred on principal planes when tested in torsion and on shear planes when tested in uniaxial tension. The mechanism transition is interpreted in terms of deformation mode and microstructural instability. In general, there was a more pronounced decrease in life with increasing temperature for uniaxial specimens than for torsional specimens. This result is interpreted in terms of an environmental interaction that is accelerated by a comparatively significant dilatational strain component.