A survey of all episodes of invasive Haemophilus influenzae infections that were diagnosed over a three-year period in children seen at the regional hospitals of the Northern Territory has found a significantly (P less than 0.001) higher incidence in children in Central Australia (the Alice Springs and Barkly regions, and the Anangu Pitjantjatjara Lands) than in the Top End (the Darwin, East Arnhem and Katherine regions), and a greater incidence in Aboriginal than in non-Aboriginal children. Identified risk factors for Aboriginal children were infancy (more than 70% of cases occurred before 12 months of age), sex (with a predominance in girls) and residence in Central Australia; the estimated annual incidence for Central Australian Aboriginal children was 991 cases per 100,000 children. There was a significant correlation (r = 0.62) between the total number of cases diagnosed each month in Central Australia and the mean monthly temperatures recorded in Alice Springs. Whereas virtually all cases of invasive H. influenzae infection in non-Aboriginal children were caused by type b strains, strains other than type b caused 15% of the cases in Aboriginal children. The possibilities for prevention by immunization are discussed.