Chemical irritants useful as repellents for brown treesnakes (Boiga irregularis) were identi®ed. Exposure to various compounds produced a range of intensities for locomotory behavior in snakes. Essential oils comprised of 10 g liter À1 solutions of cedarwood, cinnamon, sage, juniper berry, lavender and rosemary each were potent snake irritants. Brown treesnakes exposed to a 2-s burst of aerosol of these oils exhibited prolonged, violent undirected locomotory behavior. In contrast, exposure to a 10 g liter À1 concentration of ginger oil aerosol caused snakes to locomote, but in a deliberate, directed manner. We also tested speci®c compounds, all derivative of food and¯avor ingredients. 10 g liter À1 solutions delivered as aerosols of m-anisaldehyde, trans-anethole, cineole, cinnamaldehyde, citral, ethyl phenylacetate, eugenol, geranyl acetate or methyl salicylate all acted as potent irritants for brown treesnakes. The individual ingredients were classi®ed using cluster analysis into groups that promoted different levels of response by snakes. This study is the ®rst to systematically investigate the irritant potential of natural products for snakes. These data will be useful in the development of practical pest management tools for snakes.