Because the organ transplantation is currently involving patients with Chagas' disease, we evaluated the therapeutic activity of benzonidazole in mice immunosuppressed by cyclosporine and prednisone. The purpose was to obtain further knowledge regarding the infection with Trypanosoma cruzi when the immune system is depressed. It was verified that benzonidazole, at least in the conditions of the present study, decreased the severity of the parasitic component of the infection and of the inflammatory process; it has not protected the animals, that died at the same proportion in the treated and non-treated series.