Prior studies show that melatonin enhances the immune response. This study investigated the possible therapeutic effects of melatonin during the course of Trypanosoma cruzi infection. T. cruzi‐infected male Wistar rats were orally treated with 5 mg/kg body weight/day of melatonin. Animals treated with melatonin showed a significant reduction in the number of blood trypomastigotes during the acute phase of infection compared with untreated animals (P < 0.05). A significant increase in leucocytes numbers during the peak of parasitaemia was also observed (P < 0.05). Moreover, both prior and concomitant treatment with melatonin increased interleukin‐2 levels, especially 9 days postinfection (P < 0.05). Histopathological observations of heart tissue revealed that melatonin administration also resulted in fewer and smaller amastigote burdens, and less inflammatory infiltrate and tissue disorganization, indicating a reduced parasitism of this tissue. These results show that melatonin is effective in controlling parasite replication and suggest that melatonin might serve as an effective therapeutic agent in the treatment of American trypanosomiasis.