Cineole (eucalyptol) is the isolated active agent of eucalyptus oil. Traditionally, it is recommended for treating the symptoms of airway diseases exacerbated by infection. We have examined the inhibitory effect of 1.8-cineole on LPS-and IL1beta-stimulated mediator production by human monocytes in vitro. For the first time, we report on a dose-dependent and highly significant inhibition of production of tumor necrosis factor-alpha, interleukin-1beta, leukotriene B4 and thromboxane B2 by 1.8-cineole. In summary, this is the first report on a new mechanism of action of monoterpenes suggesting 1.8-cineole as a strong inhibitor of cytokines that might be suitable for longterm treatment of airway inflammation in bronchial asthma and other steroid-sensitive disorders.