Aromatherapy began in the ancient Egyptian Era and has been practiced up to the present time.  It has a long history, and yet scientific evidence supporting the efficacy of the use of plant-derived essential oils (EOs) against psychiatric disorders has not been well established.  Here, we systematically examined the pharmacological effects of EOs on the central nervous system (CNS), and found that rose oil and lavender possess anticonflict effects, and that peppermint increases ambulatory activity in mice.  We subsequently identified 2-phenethyl alcohol and citronellol as pharmacologically active constituents of rose, and 1,8-cineol, menthone, isomenthone, menthol, pulegone, menthyl acetate and caryophylenne as active constituents of peppermint.  Intravaneous administration of menthol also increases the ambulatory activity in mice, suggesting that peppermint produces its effect after absorption of its constituents into the blood stream.  Pharmacological analyses of the effects of menthol suggest that the neurotransmitter, dopamine, might be involved in the ambulation-promoting effect of menthol.  These findings support our hypothesis that EOs possess pharmacological effects on CNS functions.