Abstract: The individual time-course of the seizure threshold (ST) in electroconvulsive therapy is mostly unknown. It is assumed that a typical seizure is followed by a short refractory period and that ST increases in the long run. We hypothesize ST to be lowered immediately after the refractory period, particularly after inadequate or abortive seizures where risk for prolonged seizures is generally higher. Ketamine anesthesia does not possess pronounced anticonvulsive properties like propofol, etomidate, thiopental, or methohexital. It is therefore ideal to test such a hypothesis. We report the case of a geriatric patient with a major depressive episode, who received 5 consecutive electroconvulsive therapies with S-ketamine, all with identical right unilateral high-energy stimulation and restimulation. Whereas all primary stimulations were inadequate, all restimulations showed significantly improved seizure parameters such as midictal amplitude, maximal postictal heart rate, and average seizure energy index. In this patient, the refractory period turned out to be longer than 1 minute, and ST was lower in all 5 instances of restimulation. This ST decrease could be clinically useful in one-session restimulations.