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ABSTRACTHigh treatment failure rates for Plasmodium falciparummalaria have been reported in Colombia for chloroquine, amodiaquine, and sulfadoxine-pyrimethamine. Artemisinin combination therapies were introduced in 2006 in Colombia, where artemether-lumefantrine (AL) is currently used to treat uncomplicated P. falciparummalaria. Artemisinin (ART) resistance was initially observed in Southeast Asia as an increased parasite clearance time, manifesting as a positive thick-blood smear on day 3 after treatment (D3 positivity). Recently, mutations in the propeller domain of the P. falciparumkelch13gene (K13propeller) have been associated with ART resistance. In this study, we surveyed AL effectiveness at D3 and molecular markers of drug resistance among 187 uncomplicated P. falciparumcases in 4 regions of Colombia from June 2014 to July 2015. We found that 3.2% (4/125) of patients showed D3 positivity, 100% (163/163) of isolates carried wild-type K13propeller alleles, 12.9% (23/178) of isolates had multiple copies of the multidrug resistance 1 gene (mdr1), and 75.8% (113/149) of isolates harbored the double mutant NFSDD mdr1haplotype (the underlining indicates mutant alleles). These data suggest that ART resistance is not currently suspected in Colombia but that monitoring for lumefantrine resistance and AL failures should continue.