Fifty-two patients with American cutaneous leishmaniasis (ACL) from the Pacific coast of Ecuador were treated topically with an ointment containing 15% paramomycin (PR) and 12% methylbenzethonium chloride (MBCL) in vaselinum album (white soft paraffin; white petrolatum). After 20 applications (over 10 or 20 d) all lesions showed complete epithelialization within the first 100 d. Five patients developed new lesions during the one year observation period; 2 of these were probably reinfections. Considering all 5 cases as treatment failures, the healing rates were: 72% after 50 d, 90% after 100 d, and 85% after 360 d. In a separate study in the same area, a group of 23 patients was left without treatment for 3 months. Only 9% of the untreated patients healed spontaneously after 50 d. Growth of the lesion, inflammation and pain were observed at the beginning of treatment. After treatment, most lesions healed rapidly without scars. The drug was well accepted by the patients and was easy to administer under tropical field conditions.