This paper dels with natural Toxoplasma infection of Macacca mulatta and Cebus apella. Both monkeys died after a short period of disease and had been infected in captivity, the first one in the laboratory, probably from other mammals with experimental toxoplasmosis, and the second one in its master´s house in one of the suburbs of the city of Rio de Janeiro, where it used to eat raw meat. In this there are living other monkeys, amongst them 2 Cebus libidinosus (a couple) presenting positive Sabin-Feldman reaction (1:64) as well as the monkeys'ward. The two monkeys'histopathological examination demonstrated necrotic lesions in the liver and the spleen, and these lesions presented toxoplasmes either free or intracellular, single or associated in moderate numbers. In the Cebus there existed necrotic lesions as well as parasites in the adrenals. In the encephalous we found moderate lesions without toxoplasmes. Severe peneumonia was found in both monkyes, but only in the Cebus'lung there were seen toxoplasmes. The Cebus also had Sarcocystis in the heart. A review of natural infections of non-human Primates by Toxoplasma was made. During more than 60 years there have been described spontaneous toxoplasmosis in 31 individuals of 18 species: 3 Prosimii, 10 Platyrrhinus and 5 Catharrhinus. The low frequency of spontaneous Toxoplasma infection in the Platyrrhinus may be due to the fact that they are easier be demesticated and thus their alimentary habts are changed.