Two different strains of mice (AKR and NMRI-IVIC) were inoculated intraperitoneally with the virulent Y strain of Trypanosoma cruzi, and then treated with the lysosomotropic ethidium bromide-DNA complex, according to several different treatment schedules. When animals were treated 48 hours after intraperitoneal inoculation with three intraperitoneal doses of EB-DNA no parasitemia was detected, even after 11 weeks, confirming previous results. However, when infection was allowed to become fully established, that is 3–4 weeks after inoculation, and then challenged with several different treatment schedules (with varied doses and timing of administration) we failed to cure established Chagas' disease, suggesting that the claim of effectiveness for this EB-DNA complex is limited to early Chagas' disease.