Chloroquine resistance (CQR) is a major determinant of the present resurgence of malaria worldwide, including that of P. vivax [4] . Two main transporters have been studied in regard to CQR in P. vivax: the P. vivax chloroquine resistance transporter, Pvcrt-o, and the P. vivax multidrug resistance transporter, Pvmdr1 [5] [6] [7] . Interestingly, amino acid polymorphisms have not been associated with chloroquine resistance in pvcrt-o whereas pvmdr1 polymorphisms have been recently suggested to be associated with CQR in Southeast Asia [8] . This data indicates the involvement of other mechanisms in CQR in P. vivax. Likely candidates are gene amplifications and differential expression levels [9, 10] .