The relationship between the brain monoamines and morphine tolerance was examined in ginseng total saponins treated mice. Ginseng total saponins (100 mg/kg, i.p.) did not antagonize morphine (10 mg/kg, s.c.) analgesia in mice. Daily treatment with ginseng total saponins (100 mg/kg) did not affect the brain levels of noradrenaline, dopamine and serotonin for 5 days but inhibited the development of morphine tolerance. This inhibition of the development of morphine tolerance was not attributed to the reductions of brain noradrenaline, dopamine and serotonin in mice treated with ginseng total saponins (100 mg/kg) daily. This result suggest that a newly equilibrated state of neurologic function may involve an underlying mechanism in mice treated with ginseng total saponins.