A well-tolerated single-day treatment regimen is required for the community-based treatment of pulmonary paragonimiasis. To identify an optimal single-day treatment regimen, an open clinical trial was performed to compare the efficacy of 2 single-day regimens of triclabendazole. From 1991 to 1993, a total of 154 Ecuadorian patients were allocated to receive either a single dose or 2 doses of 10 mg/kg triclabendazole. Treatment with both regimens was associated with a rapid parasitological response (determined by clearance of Paragonimus eggs from sputum), resolution of most clinical symptoms and radiological signs, and only mild adverse effects. At 3 months after treatment, the cure rate (clearance of eggs from sputum) was 90.9% in the 2-dose group and 84.4% in the single-dose group. Re-treatment with a second 2-dose regimen was curative in all remaining patients by 1 year of follow-up. Our findings show that both single-day treatment regimens of triclabendazole were highly effective in the treatment of pulmonary paragonimiasis and suggest that patients should be re-examined at 3 months to determine the need for repeat treatment.