Trost M.E., Gabriel A.L., Masuda E.K., Fighera R.A., Irigoyen L.F. & Kommers G.D. 2009. [Clinical, morphologic and immunohistochemical aspects of canine gastrintestinal pythiosis.] Aspectos clinicos, morfologicos e imuno-histoquimicos da pitiose gastrintestinal canina. Pesquisa Veterinaria Brasileira 29(8):673-679. Departamento de Patologia, Universidade Federal de Santa Maria, Camobi, Santa Maria, RS 97105-900, Brazil. E-mail: glaukommers@yahoo.com Four suspect and two confirmed cases of gastrointestinal pythiosis were found in a retrospective study of biopsy and necropsy cases of dogs received in the Laboratorio de Patologia Veterinaria at the Universidade Federal de Santa Maria. The two diagnosed and published cases have had the etiology confirmed by culture and zoosporogenesis induction or by nested-PCR. On this study, the etiologic diagnosis of four suspect cases was confirmed by immunohistochemistry using anti-Pythium insidiosum policlonal antibody. Epidemiology, clinical signs, gross and microscopic lesions, histochemistry, immunohistochemistry, and differential diagnoses are reported and discussed.