From 1991 to 1995, eight New World nonhuman primates of the family Callitrichidae belonging to the collection of Fundacão Parque Zoologico de São Paulo died of toxoplasmosis. Of the eight affected nonhuman primates, four were Leontopithecus chrysomelas (one male, three females) and four were Saguinus imperator (two males, two females). The most commonly affected organs were the lungs, liver, and lymph nodes, with hemorrhagic and necrotic lesions. Histopathologic examination revealed protozoa that were morphologically consistent with Toxoplasma gondii. Immunohistochemical assays were strongly positive for T. gondii.