Peritoneal exsudates and organs from 53 male albino mice, experimentally infected by Toxoplasma gondii were studied, 21 at the acute phase of infection, and 32 at the chronic phase. Peritoneal inoculations were made with 0,5 ml of peritoneal exsudates (tachyzoites), or brain macerates (cysts) of previously infected mice. Direct examinations of peritoneal exsudates (tachyzoites) were realized between 3 to 12 days post-inoculation, and in brain (cysts) after 10 days post-inoculation. Organs macerates were inoculated in new mice, for the parasite recovering, from exsudates or from brains. At the acute infection (3 to 12 days) the positivity at the direct examination was: peritoneal exsudate 19/19, lung 12/14, muscle 6/9, heart 4/9 and brain 1/3. After inoculation: peritoneal exsudate 5/5, heart 9/9, lung 13/13, muscles 14/17 and brain 2/2. Then, there were 9 new positive organs. At the chronic infection, between 10 and 495 days, the positivity was, at direct examination: brain 28/32, heart 0/4 and muscle 0/4. After inoculation: brain 6/6, heart 14/29 and muscle 16/26. After that a new positive mouse was detected, which leads to 29 the positivity for all mice, or 90,6%. Finally the positivity for the acute phase was: peritoneal exsudate 19/19 (100%), heart 15/17 (88,5%), muscle 12/14 (85,7%), lung 14/14 (100%) and brain 2/3 (66,6%). For the chronic phase: brain 28/32 (87,5%), muscle 16/28 (57,1%) and heart 14/31 (45,1%). At the end of experience, at the 495th day, the brain still presented large cysts by direct examination and also the heart and muscle were positives after inoculation. Conclusions: 1st) on mice the Toxoplasma gondii remained for 495 days, mainly on the brain, but also on heart and muscle; 2nd) the lungs direct examination could be useful as substitute of the peritoneal exsudate examination; 3th) organs inoculations are necessary for the discovery of new infected mice; 4th) the cyst activity was demonstrated by its gradative increase during the chronic infection, and by its recovery in tissues after a long time.