AbstractLow cycle fatigue properties of austenitic steels and aluminium alloys are discussed. Curves of stress S–number of cycles to failure N for three alloys are presented. The form of the S–N curve is described and the various equations used by designers to represent the curve are discussed. It is suggested that microstructurally related parameters could be inserted in these parametric design equations. Attempts at achieving this objective using a disclocation stress and a fracture toughness related model are described. It is shown that reasonable fits between predicted and experimental S–N curves result from the application of the dislocation stress model, whereas the fracture toughness approach seems less successful.MST/1163