A 2-year-old, male, red-necked (Bennett's) wallaby (Macropus rufogriseus) from a zoological facility was presented for peracute onset of severe depression, unresponsiveness, ataxia, and loose feces. Serum biochemical abnormalities included azotemia, hypoalbuminemia, increased alanine aminotransferase activity, hyperbilirubinemia, hyperphosphatemia, and hyperkalemia, consistent with multi-organ system failure. Severe thrombocytopenia suggested possible disseminated intravascular coagulation. Peripheral blood smear examination revealed numerous ovoid, protozoal inclusions within monocytes and occasionally within neutrophils. Despite aggressive supportive therapy, the patent died within 5 hours of presentation. Gross necropsy and histopathologic findings included severe multifocal necrotizing lesions in multiple organs. Numerous intralesional protozoal organisms were observed and were identified as Toxoplasma gondii by immunohistochemistry. Macropods (wallabies and kangaroos) are known to be highly susceptible to toxoplasmosis, with high mortality rates; diagnosis most often is obtained at necropsy. Detection of protozoal organisms in peripheral blood leukocytes is reported rarely and has not been documented previously in a macropod. Parasitemia in this case was attributed to severe, disseminated disease. Careful examination of peripheral blood smears in macropods suspected of toxoplasmosis may be warranted.