Scale cracking and spallation behaviour under repeated thermal cycling has been studied for Haynes 214 and 20Cr25NNb for a spectrum of temperature ranges. Both alloys show an increase in the rate of mass gain after a small number of cycles in most cases. Continued cycling of Haynes 214 eventually results in spallation but this is not observed in the 20Cr25NiNb alloy. The increase in the rate of mass gain is consistent with predictions for FE models.