Free and liposome-encapsulated amikacin are active in vitro against intracellular Mycobacterium avium complex (MAC). To examine whether liposome-encapsulated aminoglycosides might kill intracellular MAC more effectively in vivo, beige mice were infected with MAC strain 101 (serotype 1) and after 1 week were treated intravenously every other day (5 doses total) with amikacin liposomes (0.2, 1, or 4 mg/dose), amikacin solution (0.2, 1, or 2 mg), gentamicin liposomes or gentamicin solution (0.2 or 1 mg), placebo liposomes (without aminoglycosides), or buffer. Amikacin and gentamicin liposomes significantly reduced bacterial counts in blood, liver, and spleen (98.5%, 92.7%, and 92.8%, respectively, for the 1-mg dose of amikacin and 92.8%, 99.7%, and 99.4% for gentamicin; 95.7%, 69.7%, and 89.1%, respectively, for the 0.2-mg dose of amikacin and 49.9%, 76.7%, and 89.1% for gentamicin) compared with placebo liposomes and buffer. Equivalent doses of free drug were not associated with significant decreases in viable bacteria. Thus, aminoglycoside liposomes improved bactericidal effects over conventional treatment in disseminated MAC infection, offering potential application in treating MAC infection in humans.