Serological examination for Toxoplasma gondii in human blood samples and in blood samples from ten different species of animals obtained in Manaus, State of Amazonas-Brazil, are compared with results obtained from similar examinations of blood from humans living in other areas of the Amazon basin. The domestic cat (Felis catus) showed the highest levels of antibody for Toxoplasma gondii, whereas the domestic chicken (Gallus domesticus) and duck (Cairina sp) the lowest. The other animals showed similar intermediate levels of antibody to this protozoa. The authors discuss the results and several aspects of the involvement in epidemiology of toxoplasmosis and call attention to some transmission mechanisms not yet elucidated.