To survey the Aboriginal community of the Northern Territory for antibodies to human T-lymphotropic virus type I (HTLV-I) and to describe the distribution of the virus.

A sero-epidemiological study using the Serodia particle-agglutination assay, indirect immunofluorescence and western blot. Evidence of HTLV-I-related diseases was sought through clinicians, and by searching the cancer register and medical records. SERA: Samples from 1897 Aborigines, including 1569 sera received by the Royal Darwin Hospital Pathology Department for syphilis serology between March and July 1988. Most of the specimens were from public health surveys and antenatal screening.

Ninety-four samples (5.0%) were positive by the particle-agglutination assay method but only 36 (1.9%) were positive by both particle-agglutination assay and indirect immunofluorescence. After confirmation by western blot, the seroprevalence of HTLV-I was 1.7% (95% confidence interval, 1.2-2.3%). Western blot positivity was higher in samples from the "Cattle Country" and Alice Springs regions (i.e., 4.7% and 13.9% respectively).

HTLV-I is endemic among Aborigines in inland Australia. These serological findings are supported by the recognition of two cases of adult T-cell leukaemia/lymphoma in this population.