The activities of four amphotericin B formulations, Fungizone, AmBisome, Amphocil, and Abelcet, were compared in vitro and in vivo against Trypanosoma cruzi infections. In vitro, Fungizone and Amphocil were highly active against T. cruzi Y strain amastigotes in macrophages with 50% effective dose (ED50) values of 0.027-0.028 microg/ml, which were 7-fold and 42-fold more active than AmBisome and Abelcet, respectively. In vitro activities of all formulations against T. cruzi amastigotes in Vero cells were similar, with ED50 values in the range of 2.0-4.2 microg/ml. Acute infections of the T. cruzi Y strain in BALB/c mice were suppressed in all animals by a single 25 mg/kg dose of the liposomal formulation AmBisome. At the same dose, the two other lipid formulations, Amphocil and Abelcet, increased the survival rate but did not suppress infection in all animals.