ABSTRACT Chagas disease is caused by the parasite, Trypanosoma cruzi, and affects millions of people in Latin America. Lately, Chagas disease has become an emerging worldwide public health issue due to globalization. Chagas disease has two phases: an initial acute phase, usually with nonspecific symptoms or asymptomatic, and a lifelong chronic phase, which is clinically silent or indeterminate in 60-70% of patients. However, 30-40% of chronic patients will eventually develop heart and/or digestive complications. Currently, the only approved drugs for treating Chagas disease are benznidazole (BZN) and nifurtimox (NFX). The efficacy of these drugs is variable and depends on the disease stage, drug dose, age of patients, and infecting T. cruzi strain(s). Treatment in the acute phase is effective with both drugs. However, the efficacy of these drugs in adults with chronic, long-established infections is significantly lower and variable. Moreover, the high rate of adverse events of these drugs has hampered their regular clinical use, thus <1% of patients are being treated. In this project, we propose to test four new dosing regimens of BZN and NFX. Our first hypothesis is that a lower frequency of BZN and NFX dosing, with standard or extended treatment duration, might have the same or better efficacy than the standard treatment regimens with these drugs, with fewer adverse events. Here, we plan to analyze current and novel host- and parasite-derived BMKs that have shown promising results in pilot, full clinical trials or in animal studies, providing a measure of disease state and cure. Thus, our second hypothesis is that in those patients that respond to BZN or NFX treatment the serum levels of one or more proposed BMKs will be significantly reduced or become negative within three years post-treatment. To test these two hypotheses, we propose two specific aims: Specific Aim 1: To determine the safety and efficacy of extended benznidazole or nifurtimox treatment regimens with lower dosing frequency. Specific Aim 2: To evaluate host- and parasite-derived biomarkers for the follow-up of Chagas disease chemotherapy. The information gained in this project would also allow for better-designed clinical trials with previously proposed drug combinations, in which BZN and NFX would play a central role.