Giardisis is a major cause of infectious diarrhoea in humans and livestock worldwide. There are currently a limited range of drugs available for chemotherapeutic treatment of this disease, with the majority of these used only following clinical diagnosis and generally not for prophylaxis. These drugs are ineffective against some of the life stages of the pathogenic protozoa, have unpleasant and unwantedside effects and may have limited availability in developing countries. Frequent reports of drug toxicity, treatment failure and parasite resistance also highlight the importance to develop new chemotherapeutic treatments with greater efficacy and less severe side effects.