Fungal infections remain a major cause of treatment failure and death in acute leukemia. New liposomal preparations of amphotericin B are now available. While less toxic, their comparative efficacy and toxicity profiles are unknown. In this study the comparative efficacy and safety of ABLC vs. AmBisome was evaluated in seventy-five patients with leukemia who developed 82 episodes of suspected or documented mycosis, and were treated (1:1) with either ABLC (n=43) or AmBisome (n=39). Both drugs were dosed accordingly from 3 to 5 mg/kg/day. Using an intent-to-treat analysis, the overall response to therapy was 27/43 (63%) for ABLC and 15/39 (39%) for AmBisome (p=0.03). Median dose and duration of treatment was 10 days at 3 mg/kg for ABLC and 15 days at 4 mg/kg for AmBisome. Acute, not dose-limiting infusion side effects were seen in 70% vs. 36% (p=0.002), ABLC vs. AmBisome. Increase of bilirubin > 1.5 times from baseline was 38% vs. 59%, ABLC vs. AmBisome (p=0.05). ABLC and AmBisome were equally effective for the treatment of suspected or documented fungal infections. While, acute infusion-toxicity was greater with ABLC, infusion toxicity requiring discontinuation was similar for both drugs. AmBisome was better tolerated than ABLC but was associated with mild abnormalities in liver function tests at the end of therapy.