The flagellated protozoa Giardia duodenalis is the most commonly detected parasite in the intestinal tract of humans. Infections with the parasite result in diarrhoeal disease in humans and animals, with infants at risk from failure-to-thrive syndrome. The incidence of giardiasis worldwide may be as high as 1000 million cases. Current recommended treatments include the nitroheterocyclic drugs tinidazole, metronidazole and furazolidone, the substituted acridine, quinacrine, and the benzimidazole, albendazole. Paromomycin is also used in some situations, and nitazoxanide is proving to be useful. However, treatment failures have been reported with all of the common antigiardial agents, and drug resistance to all available drugs has been demonstrated in the laboratory. In addition, clinical resistance has been reported, including cases where patients failed both metronidazole and albendazole treatments. The identification of new antigiardial drugs is an important consideration for the future, but maintaining the usefulness of the existing drugs is the most cost-effective measure to ensure the continued availability of antigiardial drugs.