The effect of a two-week regimen of topical aminosidine was investigated in a randomized, double-blind, placebo-controlled trial of 251 selected Iranian patients with zoonotic cutaneous leishmaniasis. Patients underwent clinical and parasitologic assessment before and 15 (end of therapy), 45, and 105 days after starting the treatment. Aminosidine ointment was safe and well-tolerated, and produced significant reductions in the prevalence of parasitologically positive smears on days 15 and 105 (but not day 45) after treatment compared with placebo. However, there was no clear clinical benefit at any stage after treatment. We conclude that this twice a day two-week regimen of aminosidine was inadequate to accelerate the recovery of most cases of cutaneous leishmaniasis. However, the ointment did show some clear evidence of parasitologic efficacy and should now be studied in longer or more frequent regimens in an effort to prevent parasitologic relapse and thus promote clinical improvement.