Abstract—A test facility has been developed in which a thin walled tube can be subjected to fully reversed fatigue cycles for all biaxial stress or strain ratios. Twin loop servo‐control allied to high resolution gauge length extensometry, load and pressure transducers permits stress or strain controlled testing. The rig is unique in that cyclic stress‐strain hysteresis loops can be obtained for both axial and circumferential directions during a test.Results from a strain controlled series of low cycle fatigue tests on a ferritic 1Cr‐Mo‐V steel obeyed the Manson‐Coffin relationship with the exponent being sensibly constant for all strain ratios. For a given maximum principal biaxial strain, the damaging effect increased as the strain ratio φ increased from –1 to +1. By comparing results from solid and hollow cylindrical specimens, geometry effects on fatigue life were revealed. Data on shakedown and cyclic softening under biaxial strain conditions were