Oral chloroquine tablet (25 mg base/kg divided to be given over 3 days; day 0, 5 mg base/kg per/meal for 3 meals; day 1, 5 mg/kg; day 2, 5 mg/kg). In this trial, we study the efficacy of chloroquine alone for the treatment of uncomplicated vivax malaria. So we give Primaquine after study finished. The standard treatment of vivax malaria patient in Thailand is 25 mg base/kg divided to be given over 3 days plus primaquine 20 mg base taken daily for 14 days.