The relations between immunosuppression and human or experimental infection by Trypanosoma cruzi have recently been the subject of great interest, specially because of the wider use of drugs acting on immunity and of organ transplantation programs, now in frank expansion. The use of cyclosporin turned necessary to know adequately its interactions with T. cruzi parasitosis, and this has been the objective of the present study, regarding the acute phase in mice, in comparison to the use of prednisone. It was verified that cyclosporin, alone or associated to the corticosteroids, promotes and enhancement of the parasitosis, as shown by the assessment of parasitemia, the amount of amastigote forms in the heart and the severity of cardiac inflammation. Such observations may be useful in clinical practice, calling the attention for necessity of a strict control of such cases an eventually the use of an antiparasitic agent.