OBJECTIVE Anesthesia is required for both magnetic seizure therapy (MST) and electroconvulsive therapy (ECT), although it has anticonvulsant properties. In this case, bispectral index (BIS) monitoring, a specific electroencephalogram-derived monitoring, can be used to find the optimal seizure induction time during anesthesia to elicit adequate seizures. A measurement of seizure adequacy in electroencephalogram is the postictal suppression. The purpose of this study was to investigate the influence of seizure induction time on the degree of postictal suppression by comparing BIS versus no-BIS monitoring in MST and ECT. METHODS Twenty patients with treatment-resistant depression were randomly assigned to either MST or ECT. Each patient underwent 3 treatments with the determination of seizure induction time by defined prestimulation BIS (BIS condition) and 3 treatments with determination of seizure induction time by controlled clinical trial protocol (no-BIS condition). Statistical analysis was calculated by repeated-measures analysis of variance. RESULTS The degree of postictal suppression was more pronounced in both MST and ECT, with BIS monitoring. In this connection, no differences between MST and ECT were found. Seizure induction time was significantly later in the BIS condition (181.3 ± 6 seconds) compared with the no-BIS condition (114.3 ± 12 seconds) (P < 0.001). CONCLUSIONS Adequacy of seizures, in the form of the degree of postictal suppression, was superior by determining the seizure induction time with BIS in both MST and ECT. Further research is needed to investigate the correlation between the degree of postictal suppression and treatment response.