Giardia intestinalis (15.2%) and Hymenolepis nana (20.4%) were the two most frequently reported species in a study of intestinal parasites from 1683 Aboriginal people in Western Australia. Concurrent infection with the two species was statistically significant in the 0 to three years age group only (P < 0.01), and it is suggested that in older age groups the presence of one of these parasites may in some way inhibit the development of the other. Hymenolepis nana infection was more common in males than in females (P < 0.001). Hookworm and Strongyloides stercoralis infections were confined to the tropical north of the State. The total or near-total absence of infection with Ascaris lumbricoides, Trichuris trichiura and Entamoeba spp. (all frequent in eastern Australian Aboriginal communities) is noted, and possible reasons are discussed.