Giardiosis is a neglected parasitic disease that produces diarrhoea and different degrees of malabsorption in humans and animals. Its treatment is based on derivatives of 5-nitroimidazoles, benzimidazoles, nitrofuranes, acridine and nitrotiazoles. These drugs produce undesirable secondary effects, ranging from a metallic taste in the mouth to genetic damage and the selection of resistant strains; therefore, it is necessary to develop new therapeutic alternatives. We demonstrated that a 2-h treatment with 2·87 μg ml(-1) of fraction 6 of Lippia graveolens (F-6) was sufficient to kill half of an experimental Giardia intestinalis (Syn. G. duodenalis, G. lamblia) population, based on the reduction of MTT-tetrazolium salt levels. F-6 breaks the nuclear envelope and injures the ventral suckling disc. The major compounds of F-6 were characterized as naringenin, thymol, pinocembrin and traces of compounds not yet identified. The results suggest that Lippia is a potential source to obtain compounds with anti-Giardia activity. This knowledge is an important starting point to develop new anti-giardial drugs. Future studies will be required to establish the efficacy of F-6 in vivo using an animal model.