To determine if antibodies to rickettsiae (scrub typhus, spotted fever, and typhus group rickettsiae) occur among persons living in the Kimberley (northern tropical) region of Western Australia, 920 sera collected in a non-random manner in 1996 from patients in Kununurra, Broome, Fitzroy Crossing, Wyndham, Derby, and Halls Creek were tested by micro-immunofluorescence for antibodies to a panel of rickettsial antigens. Of 920 sera examined, 52 (5.6%) were positive for antibodies to one or more of the three groups of rickettsial microorganisms. The largest group of sera (24; 2.6%) were positive for scrub typhus (Orientia tsutsugamushi). Eleven other sera (1.2%) were positive for scrub typhus and spotted fever group rickettsiae and four (0.4%) were positive for scrub typhus, spotted fever group, and typhus group rickettsiae. In addition 13 sera (1.4%) were positive only for spotted fever group rickettsiae. In this study, only titers > or = 1:256 were considered significant. Thus, there is serologic evidence for scrub typhus and spotted fever group rickettsial infections in the Kimberley region of Western Australia. Because of the method of serum collection, it is not possible to determine the prevalence of seropositivity, but the data support the need for a proper epidemiologic study of rickettsial diseases in this region of Australia.