Pentavalent antimony has been considered to be the standard treatment for leishmaniasis, but more recently, the orally administrable agent allopurinol ribonucleoside has been the subject of several clinical trials. In this study, these two agents were evaluated in patients with Ecuadorian cutaneous leishmaniasis. Patients were randomly assigned to the two treatment groups. The mean reduction in lesion size for the 28 patients treated with Pentostam (20 mg Sb/kg/day intramuscularly for 20 days) was 61%, 23%, and 11% after one, two, and three weeks, respectively. There was a wide range in the individual values, and some lesions markedly enlarged in the first week of therapy. An initially healed lesion was defined as one that had greater than 80% re-epithelialized by the 1.5-month post-treatment followup. All Pentostam patients demonstrated this degree of lesion resolution (100% initial healing rate), but one patient showed evidence of relapse at the three month followup resulting in a 96% complete healing rate for the 12 month observation period. Patients in the untreated control group demonstrated a strikingly high rate of healing with 9 of 12 patients having re-epithelialized all lesions after 1.5 months observation (75% initial healing rate). The mean reduction in lesion size for the untreated patients was 56%, 29%, and 25% after one, two, and three weeks, respectively. Twenty-one patients received allopurinol ribonucleoside (1,500 mg QID) plus probenecid (500 mg QID) for 28 days. Lesions in nine of these patients were healed at the time of the 1.5 month followup (41% healing rate).(ABSTRACT TRUNCATED AT 250 WORDS)