Muscle action potentials elicited by paired transcranial magnetic stimulation were recorded during spine surgery in 34 patients. Anesthesia was based on ketamine and fentanyl. To evaluate the optimal anesthetic regimen to be used for transcranial magnetic stimulation, and to determine the clinical import of magnetic-evoked compound muscle action potentials. Muscle action potential by transcranial magnetic stimulation has been difficult to record under general anesthesia. Ketamine is known to not suppress the muscle responses, although no conclusive clinical study has been reported. Paired transcranial magnetic stimulation was delivered as muscle action potentials were recorded from the limb musculature. Neuromonitoring was reliable in 56% of total cases and in 82% of the recent cases after reducing fentanyl dosage. Paired magnetic stimulation was an excellent facilitation technique for reliable monitoring. At higher dosages, fentanyl and ketamine decreased the reproducibility of the responses. Magnetic-evoked compound muscle action potential neuromonitoring is a sensitive and selective motor pathway monitoring method that covers the entire motor pathway, including the white and gray matter of the spinal cord. Ketamine-based anesthesia is a good choice for this purpose.