The phenomenon of low-cycle fatigue was investigated with total strain ranges from 1 to 2 pct and frequencies from 0.2 to 100 cpm. Changes in endurance life under varying strain and frequency conditions were determined. During the endurance tests moment and strain values were recorded. From the continuous time recordings of these parameters, elastic and plastic time ratios of specimen lives were defined and their dependence on strain and frequency levels found. The change in crack propagation rate with frequency was also studied. Finally, a cumulative fatigue hypothesis, incorporating both frequency and strain parameters, was formulated and shown to be valid under varying strain and frequency conditions.