The increasing performance requirements of gas turbines are driving higher operating temperatures in critical components, leading to greater creep and fatigue interactions. There is thus a requirement for thermomechanical fatigue (TMF) test data, including TMF crack growth rates. The test equipment required to meet this challenge is briefly discussed, along with the development of the test methodology. Thus, the accurate measurement and maintenance of thermal performance during TMF are considered. The determination of fatigue crack growth rates by conventional electrical potential difference measurements has been employed, utilizing convenient dwells within the TMF cycles, where both load and temperature are held constant for a brief period. These experimental methods have been demonstrated with trials on the advanced nickel base superalloy RR1000 used for turbine discs. This work has also highlighted significant microstructural effects on the crack growth rates, with the coarser grain size offering a reduced crack growth rate.