An avirulent T. gondii strain isolated from a owl (Glaucidium brasilúmum) produces randomIy distributed cysts in the brain of mice which can survive to inocula as high as lOOO oocysts. Cysts appeared for !he first time afler 15 days of infection. Regarding to humoral inununity development due to our TCR-2 strain, detectable antibodies were found after 12 days of infection.