The authors made a study of the infection behaviour of a T. cruzi strain - Bolivia strain - through the inoculation of leishmania and flagellates forms from culture (Warren media) in white baby mice. They have used the prepatent period, the infection index, the parasitemia during the acute phase and the death rate for the evaluation of the infectious process. The results showed different characteristics of the infection when are used one or the other kind of inoculation.