The prevalence of Toxoplasma gondii in indigenous Brazilian tribes with different degrees of acculturation was studied in the Enawenê-Nawê, an isolated tribe, in the state of Mato Grosso, the Waiãpi, with intermittent non-Indian contacts, in the state of Amapá, and the Tiriyó, with constant non-Indian contacts, in the state of Pará. An IgG−enzyme-linked immunosorbent assay (IgG-ELISA) or an IgG/IgM−indirect immunofluorescence antibody (IFA) assay were performed for the detection of antibodies to T. gondii in 2000−2001. Both assays showed that the Tiriyó had the lowest crude seroprevalence (55.6%), the Enawenê-Nawê the highest crude seroprevalence (80.4%), and the Waiãpi an intermediate crude seroprevalence (59.6%). The age-adjusted prevalence (95% confidence intervals) values for the Tiriyó, Enawenê-Nawê, and Waiãpi were 57.3% (53.4, 61.1%), 78.8% (72.2, 85.7%), and 57.7% (52.5, 62.9%), respectively. Contact with non-Indians probably did not influence the prevalence of the infection. However, differential contact with soil-harboring oocysts from wild felines may be responsible for the various seroprevalences in the different tribes.