Plasmodium vivax infects ~20 million people each year. Most of these vivax malaria cases occur in the Asia-Pacific region where more than 2 billion people are at risk of infection. Unfortunately resistance to the first line treatment for vivax malaria; (chloroquine) is rapidly spreading though South East Asia. Tools to reliably detect the spread of P. vivax chloroquine resistance (CQR) and determine its sensitivity to new therapeutics are urgently needed. In this proposal we seek to identify the genetic/molecular basis of P. vivax drug resistance in Vietnam and Cambodia. In doing so, we hope to provide novel markers for the rapid detection of CQR P. vivax and new therapies targeted at reversing CQR.