Methods: Amplitude and latency of TcMEPs were recorded bilaterally from the abductor pollicis brevis (APB) and abductor hallucis (AH) muscles in 38 adult American Society of Anesthesiologists I and II patients undergoing thoracolumbar spine surgery. Baseline recordings of TcMEPs in both groups were recorded under propofol infusion. Group X patients then received propofol and fentanyl (1 mcg/kg/hr), and group Y patients received ketofol and fentanyl (1 mcg/kg/hr). Bispectral index was maintained at 40–60 in both groups. Amplitude and latency were recorded at 30 minutes intervals for 2 hours. Results: Propofol caused no significant changes in amplitude and latency in any muscle. In contrast, amplitude increased significantly at all time points in the bilateral APB muscles and 60, 90, and 120 minutes in the left AH muscle without changes in latency in response to ketofol. When the two groups were compared, ketofol induced significantly higher amplitudes at 60, 90, and 120 minutes in the (left) APB, at all time points in the (right) APB, and at 120 minutes in both AH muscles, compared with propofol. Blood pressures were lower and fluid and vasopressor requirements were higher in group X. Muscle power was similar between the two groups. Conclusions Ketofol facilitates TcMEP amplitudes without affecting latency. Use of ketofol resulted in a better and more stable hemodynamic profile than did use of propofol.