This is a randomized open-label trial to evaluate the efficacy of chloroquine (CQ) alone compared to chloroquine+primaquine (CQ+PQ) in the treatment of uncomplicated malaria caused by Plasmodium vivax infection in a endemic area in the westernmost part of the Amazon Basin of Brazil. The duration of follow up for evaluating CQ efficacy as a schizonticidal drug was 28 days. The duration of complete follow up to detect recurrent P. vivax infections by passive surveillance was six months. All patients in the CQ alone arm received 7 days of PQ treatment (3.5mg/kg total dose) starting on day 28 of the study follow-up.