The work reported in this thesis is concerned with the behaviour of two high-alumina ceramics (designated 'Sintox' and 'Lucalox') under single and repeated cycles of thermal and mechanical stressing. It has been demonstrated that the materials exhibit well-defined fatigue behaviour. The fatigue curves presented each have three distinct and characteristic features, namely a high-stress plateau (tentatively referred to as an incubation region), followed by progressively increasing endurance with decrease in applied stress culminating in a fatigue limit. Evidence has been presented to demonstrate the influence of environment and surface condition on such behaviour, whilst the significance of delayed fracture (static fatigue) effects has been emphasised. Data has been presented relating to the propagation of thermal fatigue cracks, demonstrating step-wise growth of a type reported for various metallic materials. Study of the fracture surfaces of mechanically stressed alumina has indicated various cleavage 'step' and 'river' pattern features. A semi-empirical expression, based on considerations relating to accumulation of strain energy, has been deduced to describe the various fatigue curves obtained.