Background: In aromatherapy, essential oils are used as anti-inflammatory remedies, but experimental studies on their action mechanisms are very limited.Aims: To assess their anti-inflammatory activities, effects of essential oils on neutrophil activation were examined in vitro.Methods: Neutrophil activation was measured by tumor necrosis factor-alpha (TNF-α)-induced adherence reaction of human peripheral neutrophils.Results: All essential oils tested at 0.1% concentration suppressed TNF-α-induced neutrophil adherence, and, in particular, lemongrass, geranium and spearmint oils clearly lowered the reaction even at 0.0125%. Similar inhibitory activities for the neutrophil adherence were obtained by their major constituent terpenoids: citral, geraniol, citronellol and carvone. In contrast, very popular essential oils, tea tree oil and lavender oil, did not display the inhibitory activity at the concentration.Conclusion: Thus, some essential oils used as anti-inflammatory remedies suppress neutrophil activation by TNF-α at a low concentration (0.0125-0.025%) in vitro.