The technique of jerk-locked averaging was applied to two patients with pathologically proved Creutzfeldt-Jakob disease. Patient 1, whose brain contained numerous kuru plaques and severe cerebral white matter degeneration, did not show any periodic synchronous discharges in spite of frequently repeated EEG recordings. The technique of jerk-locked averaging, however, disclosed a negative sharp wave over the contralateral central area in close temporal association with myoclonus of an upper extremity. Patient 2 had classic periodic synchronous discharges on the EEG, and jerk-locked averaging delineated a fixed relationship in time and space between the periodic discharge and the myoclonus.