Reactivity feedback is an important indicator in the analysis of the dynamic behavior of a nuclear reactor. The roddrop perturbation method is used at EBR-II to produce time-dependent power data which are pro cessed with an on-line digital data reduction procedure to produce time-dependent reactivity feedback; reactivity feedback models are defined in the time and frequency domains. This streamlined procedure has resulted in decreased data reduction time and man power requirements along with increased data integrity.