Twelve dogs naturally infected with Leishmania infantum were treated subcutaneously with aminosidine at a dose of 10 mg kg-1 per day for four weeks. Antimonial compounds were used as reference drugs in twelve Leishmania-infected dogs. Eleven of the twelve dogs submitted to aminosidine therapy responded within 30 days. The treatment with the aminoglycoside antibiotic presented a marked decrease of anti-Leishmania antibody titres than the controls. Aminosidine also reduced urinary protein, serum IgG, and circulating immune complex concentrations. Side effects were observed only in a dog with pre-existent renal lesions. This study proved that aminosidine is an effective, tolerable and safe drug for the treatment of canine leishmaniasis and that it could be used as a suitable substitute for antimonial therapy.