Exposure to intrinsic Hg in fish was studied in Amazon populations with high prevalence of malaria disease. High fish-eater riverines were compared to urban (Manaus residents) low fish-eater riverines in regards to Hg exposure (hair-Hg) and serum antinuclear antibodies (ANA). Most riverines (99.0%) ate fish daily compared to only 3% of controls. Fish species high in MeHg was consumed more frequently (45.5%) by riverines than controls (18.8%). Mean hair-Hg (34.5 ppm) of riverines was significantly higher than controls (1.0 ppm). Although positive serum ANA was more frequently observed in riverine fish-eaters (12.4%) than controls (2.9%), there was no significant association between hair-Hg and ANA. High prevalence of malaria reporting among riverines was neither associated with Hg exposure nor with serum ANA. An autoimmune dysfunction is unlikely to occur as a result of MMHg exposure due to fish consumption.