Thirty-five individuals from endemic areas of Central Brazil (age range, 18-64 years; 19 women) in the chronic phase of Chagas disease, with positive serology and presence of circulating parasites detected by one or more recent positive xenodiagnosis, were selected for this study. Allopurinol (900 mg/d) or placebo was administered in a double-blind clinical trial for 60 days. After codes were broken, 23 had been allocated to the intervention group and 12 to the placebo group. Side effects were observed in 11 patients in the intervention group and in 1 in the placebo group. Seventeen patients in the intervention group and 10 in the placebo group completed the trial. Follow-up was performed by monthly xenodiagnosis and serologic tests every 3 months during the first year and at the end of the trial. Xenodiagnosis remained positive in all 17 of the treated group and in all 10 of the placebo group. Serologic tests were persistently positive in both groups after treatment. We concluded that, at the doses used, allopurinol was not effective to clear, in our region, Trypanosoma cruzi from peripheral blood of infected individuals.