Following reports of associations between autoantibodies and living in the tropics, we have studied the seroprevalence and nature of anti-nuclear antibodies, anti-cardiolipin antibodies, antibodies to extractable nuclear antigens and anti-neutrophilic cytoplasmic antibodies in 351 West Africans with malaria, tuberculosis or hepatitis B, or in good health. Amongst healthy West Africans we found a seroprevalence of 7% for anti-nuclear antibodies with several staining patterns, and of 30.3% for anti-cardiolipin antibodies. Among patients with tuberculosis and malaria there was twice that frequency of anti-nuclear antibodies (predominantly speckled in pattern), and anti-neutrophil cytoplasmic antibodies (predominantly IgM) were demonstrated in a few cases. A possible association between IgG anti-cardiolipin antibodies and tuberculosis was observed (P < 0.05), but antibodies to double-stranded DNA were not elevated and no antibodies to extractable nuclear antigens were found in any of the patients or healthy individuals studied. Our findings suggest the need for caution in the interpretation of autoantibody tests in subjects from or living in the tropics, as well as in patients with tropical infections.