Abstract Vasconcellos MSD, Batista LCSO, Vidal LGP, Passos MM. 2013. Intensidade de infecção por Isospora spp.(Apicomplexa: Eimeriidae) em trinca-ferros-verdadeiros Saltator similis d’Orbigny, Lafresnaye (Passeriformes: Cardinalidae) mantidos em cativeiro no Município de Valença, Estado do Rio de Janeiro, Brasil [Infection intensity by Isospora spp.(Apicomplexa: Eimeriidae) in green-winged saltators Saltator similis d’Orbigny, Lafresnaye(Passeriformes: Cardinalidae) kept in captivity in the Municipality of Valença, State of Rio de Janeiro, Brazil] Coccidia 1, 39-43. Departamento de Parasitologia Animal, Instituto de Veterinária, Universidade Federal Rural do Rio de Janeiro. BR-465 km 7, 23897-970 Seropédica, RJ, Brasil. E-mail: liliancsobatista@ hotmail. com Coccidiosis is considered an important cause of enteritis and death in passerines of all species, being the genus Isospora considered the most relevant coccidian parasite of Passeriformes. The aim of this study was diagnose and quantify the oocysts of the genus Isospora from green-winged saltators Saltator similis d’Orbigny, Lafresnaye kept in captivity in the Municipality of Valença, State of Rio de Janeiro. In the period from June to August of 2013 fecal samples were collected from 40 S. similis bred in captivity. Based on the morphological characteristics, oocysts of Isospora spp. were identified in 90% of the fecal samples. From these positive samples, 13 (36.1%) passerines had low infection intensity, 16 (44.4%) passerines had moderate intensity infection, and seven (19.4%) passerines had high intensity infection. These itensities of infection reveal that coccidiosis represent a threat to the health of passerines in this locality; therefore, the breeders need to be alert to handling, to predisposing factors of coccidiosis, such as poor hygiene and overcrowding, as well as the mode of transmission of this disease in order to avoid it.