The basis for such conjectures consists largely of reports on the occurrence of cases of toxoplasmosis in dogs, cats, and other animals (for review, see Callahan, Russell and Smith, 1946) and on several surveys on the prevalence of the infection in murine hosts. In the first of these surveys, Perrin, Brigham, and Pickens (1943) found 8.7 per cent of wild Norway rats in Savannah, Georgia infected. Hiilphers, et al. (1947, fide Laven and Westphal, 1950) reported finding Toxoplasma in 27 of 840 hares in Sweden. Laven and Westphal (1950) tested serologically a total of 81 rats from 3 sections of Germany and found 10 positive. Eyles (1952) examined 90 Norway rats by inoculating 18 pairs of guinea pigs each with pooled brain tissue from 5 rats and found Toxoplasma infections in 5 of the pairs. Christiansen and Siim (1951) in Denmark examined histologically a large number of hares shot in a sick condition or found dead in the field. Of 2,812 animals, they found 264 or 9.4 per cent positive for toxoplasmosis. As to birds, Toxoplasma has been reported from about 45 species, mostly on morphological evidence which is not always conclusive. It has been well established, however, by Carini (1911) and by Reis and Nobrega (1936) that the pigeon is a natural host of Toxoplasma. It was also shown by Nobrega and Reis (1942) that toxoplasmas of pigeons are capable of infecting rabbits, guinea pigs, and mice. Also, dogs and cats were infected with the same strain obtained from Reis and Nobrega by Guimaraes and Meyer (1942). In the United States, T. gondii was isolated in mice from the tissues of a healthy pigeon in Cincinnati, Ohio by Feldman and Sabin (1949). This pigeon had a dye test titer of 1 : 1024; two other pigeons, of 20 tested, showed titers of 1: 64. Manwell and Drobeck (1951) found 1 of 60 pigeons from the Syracuse, New York area positive in the dye test, and on this basis postulated a 2 per cent rate for naturally occurring toxoplasmosis in these birds. Epizootics of toxoplasmosis in pigeons have been reported from Panama (Johnson, 1943), Brazil (Springer, 1942), and the Belgian Congo (Wiktor, 1950). Our interest in pigeons as a possible reservoir of infection was aroused as a result of studies on the parasitemia in experimentally infected birds (Jacobs and Jones, 1950). Pigeons infected with the RH strain of T. gondii showed a high parasitemia even in the absence of acute disease. It was considered possible that pigeons with asymptomatic toxoplasmosis might serve for infecting bloodsucking arthropods in nature. Since these birds are ubiquitous and have considerable contact with man, it was deemed worthwhile to obtain information on the occurrence among them of natural infection with T. gondii.