Lavender (Lavandula angustifolia, P. Miller) is used in aromatherapy as a holistic relaxant and is said to have carminative, antiflatulence and anticolic properties. Its sedative nature, on inhalation, has been shown both in animals and man. Lavender has a spasmolytic activity on guineapig ileum and rat uterus in vitro and it also decreases the tone in the skeletal muscle preparation of the phrenic nerve-diaphragm of rats. As the mechanism of action has not been studied previously, the spasmolytic activity was studied in vitro using a guinea-pig ileum smooth muscle preparation. The mechanism of action was postsynaptic and not atropine-like. The spasmolytic effect of lavender oil was most likely to be mediated through cAMP, and not through cGMP. The mode of action of linalool, one of lavender's major components, reflected that of the whole oil. The mode of action of lavender oil resembled that of geranium and peppermint oils. Copyright 1999 John Wiley & Sons, Ltd.