Resistance of P. vivax to chloroquine has been reported from South-East Asia and Oceania but is probably limited in distribution. There is insufficient knowledge at present to allow specific recommendations to be made for treatment of P. vivax epidemics in areas of suspected resistance. ACTs (except artesunate + sulfadoxine-pyrimethamine) should be used for treatment as they are highly effective against all malaria species. In areas with pure vivax epidemics, and where drug resistance has not been reported, chloroquine is the most appropriate drug once the cause of the epidemic has been established.