The accumulation of fatigue damage under complex mechanical histories is approached from a cyclic deformation viewpoint. Smooth axial specimens of SAE 1045 steel in two heat treated conditions were subjected to repeated blocks of a variety of complex strain histories and the resulting stress-strain responses determined. A new damage equation, based on simple materials properties, was then applied to stabilized blocks and a fatigue life predicted. The method entails a reversal-by-reversal stress-strain analysis of a history using the ratio of plastic to elastic strain range as a damage parameter. A computer program was developed to perform the detailed data reduction and analysis and can be employed on-line in a computer interfaced, closed loop test system. Agreement between experimental and predicted lives is within a factor of two over the range of lives investigated.