The purpose of this study was to compare effects of various anesthetic drugs on expression of Fos protein in the supraspinal neurons of rats. Optimum anesthesia was maintained under monitoring of EEG. Degree of Fos expression was evaluated by counts of Fos-immunoreactive (ir) neurons. Urethane induced the largest amount of Fos-ir neurons (n = 8439), while fentanyl/midazolam the smallest (n = 112). alpha-Chloralose, halothane, pentobarbital sodium and urethane/alpha-chloralose induced amounts in between. The results indicate that fentanyl/midazolam is the most recommendable anesthetic drug in the Fos expression study.